Villain Platy

Some fish can be more aggressive than their reputation says. It is quite likely that the aggressive platy took the 'top dog' position when you got the first four, then when you added the next three he saw them as challenging his dominant position.
My maths says you added the last three platies a week ago? Has the male in question settled down at all or is he still chasing the remaining two new ones? If he is still behaving aggressively, I would think about returning him to the shop, maybe see if they'd swap him for a different male. If you can catch him.
It is easier to catch a fish if there is less water in the tank ie during a water change. Using two nets, one to chase him into the other, is also recommended though with a corner tank you might not be able to reach to the back with both nets. Other people chase the fish into a jar or plastic bag. Do you have anything that could b used to herd him into a front corner; something large with holes in for the water to pass through (like a tank divider)? Failing all those, it is much easier to catch fish if there are only 2 inches of water but with a 190 litre tank, that won't be an easy option 

Make sure the breeding box has a lid or you'll be back to square one!

You could ask other shops if they'll take him, usually with nothing in return. Or advertise on aquarist-classifieds; advertising him as free will get more response. I assume that you'll give him away to get rid of him?

I understand that a lot of branches of Maidenhead Aquatics do take unwanted fish (if you are in the UK and there's a branch near you). Or just ask in all the shops you can think of.