Stocking A 240l

120cm long. What would the German degrees of my tank be? The same as my tapwater?

I know my local hardness is 6.35 in German Degrees.

The local ph is 7.5
The local hardness in german degrees is 6.35

Fair enough. In that case I'm totally at a loss again

Unfortunately, the profile of the celebese rainbow on Seriously Fish gives the hardness range as 10 to 25 dH so your hardness isn't high enough for them.

Hardness is more important than pH when looking for a suitable species.

There is one course of action we haven't yet mentioned. Take a tour around all your local shops and see what they stock. make a note of anything that catches your eye (remembering that the fish in the shops still have some growing to do) then look them up on Seriously Fish. You could well see something that none of us have thought of.
You need fish that won't pick on the rams; fish that won't stress them by swimming too vigorously, and fish that like the same water as rams.

Ah, I'd forgotten that, sorry 

I looked at the Seriously Fish profile and didn't believe what I read. I have never heard of a fish that can live in water with such a huge hardness range - they give 0 to 268 ppm or 0 to 15 dH. My other go-to site is FishBase, and they don't give water requirements. I don't trust most of the sites found by google to give accurate information. But I did find one that was interesting http://www.iucnredlist.org/details/2721/0 If you scroll down to 'habitat and ecology' it does bear out what SF says, and this site should be reliable.

So yes, they would be suitable for your tank.

I've just looked that up and it seems you have a winner. SF's list of suitable tank mates includes rams of both species. And at 7 to 8 cm it is a bigger fish.

Now all you have to do is find some  There is always the option of on-line, though courier fees can be expensive. You mentioned Pets@Home and a garden centre - I would ask at the garden centre if they can order some in for you. The worst they can say is no. Make sure you have the latin name as well as the common name so that if they are willing to order them, they get the right fish. I have done this with my favourite shop and they have looked at their two wholesalers' websites while I've been in the shop to see if the fish I wanted were available.