I don't think I've ever seen a 38A in brick and mortar stores, but One Hanes Place (http://www.onehanesplace.com) offers a few reasonably-priced 38A bras. When I've ordered bras from them in the past, I've found the best strategy is to order several different models and sizes, try them on, and then return the ones that don't fit.

(This is reminding me that I really need to get refitted. Bleh.)