I have to buy mine online since the stores don't seem to think there are any women out there larger than a DDD cup! The best place I found that gave me the best advice on measuring and finding a good fit was Figleaves.com. They're not cheap, but the bras I've bought, based on their advice, fit me very well and last a long time. And since I have to wear the dang thing every day, or tuck myself into my pants pockets, I figure it's worth the extra dough. I watch for sales and online specials, too.
by the way, I HATE HATE HATE trying on bras in the department stores. By the time I cinch the straps up to where I need them and get myself hooked up in back, I've worked up a sweat and have a cramp somewhere in my shoulder and am about ready to pass out.
I know my insurance would cover a breast reduction, but I feel like I have to give old-fashioned weight loss a try first. The last time I went on a serious diet and exercise regimine, I lost a full cup size, so I know it would help -- I just have to DO IT!