It's difficult to find a sports bra for large breasts that doesn't have an under wire. I know they advise not to wear one for sports bras, and I can see why, but I just go ahead and wear one anyway.
I think once you get past a certain size of breast there's just no escaping the under wire. Otherwise the bra simply won't hold you in properly. It gets so that the material has to be so tight you won't be able to breathe.
The best kinds of running sports bras will have a thick pad so that the under wire won't hurt (too much anyway) and you'll usually hardly be able to tell it's there.
The one thing that annoys me about it, I have to say, is that having an under wire seems to shorten the life of the bra. It usually only takes mine a few months before the wire manages to work its way through to the outside, usually poking me in the process.
I wish someone would really sit down and design a decent sports bra for women with larger breasts.