I have this same problem.
This morning, I was at the gym and I was running. I bought a few Danskin Sports Bras from Walmart, size 42D - and this is what I had on today. It gave me ABSOLUTELY NO SUPPORT. I was running and trying to hold my boobs in because they were bouncing around too much!
I have two sports bras that have wires, and they are very supportive. I can't find them anywhere anymore, it looks like the vendor (i'm not sure who it is right off hand) stopped making them!!!
If anyone has more suggestions, keep em coming...and I think I need wires for support! Wish I could do wireless, but I'm SCARED!
I looked at the link posted above, it looks like the underarmour ones don't run very large.
