The Tribulations Of Cycling A New Tank - Need Advice

More eggs. 
Have scraped.

Poor Big Bertha, she's gotta be tired!

more eggs. same yesterday.

She's laying them faster than I can find them all!

Yeah, this can't be good for her? Laying eggs so often? I scrape them off the glass and then just don't feed the fish that day. The eggs vanish.  But if I do a large (more than a few litres) water change or mess with the internal bits of the tank very much at all (like to cut out and remove dead leaves or re-set plants in the gravel), blammo, fish orgy that night! 

On the good side, the tank seems to be starting to cycle. I've got ammonia between 1 and 2 (closer to 1, I'd say), nitrites at .25, and nitrates at 10. The pH I'm artificially propping up to just over 6 by doing a few litres of fresh water that has had dolomite sitting in it for a few days, every other day. I also put a few tablespoons of dolomite gravel and crushed coral down next to the sponge filters in the filter housing and dosed the sponges with Tetra's Safe Start Plus (which I'm told by Tetra is the same as Safe Start, just how they market it in the USA) on Friday. Three days later, I'm getting nitrate readings.

Cool. 

Does anyone know of a shop in Scotland that sells female Betta fish?

Most of the shops in Scotland are these ones https://www.fishkeeperscotland.co.uk/ and one will vary from another as to what they stock, so best to contact them individually.
Some independents include Riverside Aquaria, Central Aquatics, Waterworld Aquatics, House of Pisces, Discovery Aquatics.
Pets At Home varies from one branch to another in terms of knowledge and care of staff - it might be worth chatting to the staff at the one you've spotted the female betta in, to gauge how much knowledge/otherwise they have and where the stock and that particular betta has come from. At least they're quarantining her and other stock which is a positive sign - that may be for no reason other than precautionary.

Ok, is there some other fish, perhaps?

Just looked in the small tank, to which I'd moved some of the clippings from the large tank. There are now 5 fry in there! (Oh my.) Big Bertha has been laying eggs at least twice a week, and I'm not sure I've gotten them all. I think Big B is going to have to go back in the small tank for a while until I can sort out something to take care of all the eggs/fry!

Yeah, that's plan "A". Assuming we can catch her! (This is not going to be easy.)

I wonder if a gourami would help with the problem. My daughter saw one at the Pets-at-Home that she's been talking about. She really wants a male betta, and I've veto'd that for putting in my tank with all the corys. We had devolved down to a female betta, but if there's a chance she would be cranky to the corys (the ones we want to keep alive), it would seem some other fish would be the option.

The pH of the water is holding at about 6.4 now, which is good. But probably still too acidic for a shrimp. Which are obscenely expensive in this country anyway! We used to pay the equivalent of about 20p per ghost shrimp in the States. The only ones we've found here are like ten times that! Oh, well, I may have to just shell out for a few and see if they'll help with the problem of the eggs.  I wonder if getting a male guppy... I seem to remember guppies were omnivorous?

I'm not wild about buying an assassin, but there has to be balance in the tank or Big Bertha is going to live out her life in solitary, which is just mean.

We were going to, initially, try to get a school of flame tetras to go in there, as they are very small. Before we realized how many fry had survived. I think they might overload the tank now, though. And although they are tetras, I don't think they'd help with the overpopulation problem. The neons we have in the small tank (which has, thankfully, recycled itself) couldn't care less about fish eggs or fry. (I had read somewhere that tetras  would be good as they'd eat the fry. Maybe somebody else's fry, but ours don't. So I don't want to gamble on the flame tetras.)

Right now it's a 60litre tank, heavily planted, and has 9 albino corys in there (the three originals and the six surviving young). That I know of. There could be more.  Oh, and there's still little Rambo, the one fry that went in as an egg when we first started to cycle the tank. So 10 corys. The filter is rated for an 80 litre tank, but I don't like pushing the envelope with too many fish. (That is, after all, how we ended up with the larger tank.) When all those guys are grown, that's pretty much the limit of what that tank should have.

The daughter has wanted a betta, so that would not be an unwanted fish. She also saw a lovely gourami, but I am afraid it is a dwarf. (I know about the 20% of the ones being imported having that ghastly disease.)

Hmmm. Snail? Is there a kind of snail that eats eggs (and we also have some algae) that doesn't reproduce faster than a bunny?

I'm a doofus! I've just read back through this thread and have seen that your water is on the acidic side, so there may be problems with keeping shrimp & snails.

I'm wondering if it's worth trying to discourage the breeding behaviour in your cories. Large volume cool water changes are usually suggested as a trigger for spawning. Perhaps smaller, warmer, more frequent water changes could help to avoid this? Maybe? I understand you not wanting to keep Bertha separated from the rest of the group for ever (though it might be the only guaranteed option to avoid eggs), so we could have a look at what we could do in the tank to avoid encouraging spawning.

Picking up on a point above re snails, I have nerite snails which I keep in very soft water (along with daily supplies of Snail Stixx for their shells' sake). However, these particular snails are herbivores, so are very unlikely to eat eggs.

[Interesting that you should mention flame tetras - given their small stature, they are a possiblity for future stocking on my rather long list of possibilities.]

At this point I am wondering if there is an organization where I can adopt out some of the corys?

Some LFSs take in fish, possibly in exchange for credit.
Alternatively, you could put up an advert under the appropriate location at http://www.aquarist-classifieds.co.uk/php/county.php
Alternatively again, these folk might be able to help / members willing to take some: https://www.facebook.com/CentralAquaristSocietyscotland/