Do you mean a longline bra, or an actual corset? I think you probably mean a longline bra.
I bought mine from www.lindathebralady.com Some of theirs have padding in the cups already, but if you buy one that doesn't, your seamstress can easily add padding to the cups of the bra. That's what I did.
Websites/blogs where our wedding has been featured:
A good pair of spanx (or even control top panties) and a longline bra will do that.