For good supportive bras, anywhere past a C cup be prepared to spend a pretty penny.
You can try Lane Bryant. Sometimes they have awesome sales like BOGO or buy 2, half priced third. $40 and up, for DDD and above.
Other than that, try shopping online. Read the reviews before buying, and check for how returns work before getting it from a particular site. I've had a lot of luck with pretty much any Tish bra out there, but they are costly.