Is there anywhere in the UK where I can get a copy of the Mega Bosses?
I can't find them anywhere.
You won't find this game or any of its expansions in stores, possibly ever. Unfortunately it's pretty rare for anyone to be selling any expansions separately. I'd like to pick up the Adrenaline expansion at some point, but have to resign myself to the possibility that it will never be available.
Hopefully, the publisher changes its mind about abandoning this game, and either republishes it, or lets another publisher republish it. Time will tell, and the fact that it is getting such rave reviews (including being Tom Vasel's top game of the year) will hopefully convince them to find a way to get the game and all its expansions to the public.