I think I have seen bras like that at the Triumph shop in our town. Maybe something like this

http://www.freemans.com/Triumph-’T...asterItem&An=0

?

I had some of those as teenager and liked them:

http://www.triumph-sport-bh.de/trium...-bh-racer.html

It hooks in the front I'm not sure if that would be ok for you.