What's your budget? What style of goth are you looking for? I think Demonia and New Rocks are the most popular brands; those both have their own websites and Amazon catalogues iirc, but if you're into old-school stuff you could get a pair of winklepickers; they're unisex (so you could order in a men's size) but they also make your feet look bigger, so keep that in mind. There used to be a place in England that custom-made them called The Gothic Shoe Company. I can't find their website now, but I found a different website for "gothic pikes" that does the same thing, they're just based in Berlin instead (maybe it's the same company and they moved? idk)
I don't know of any place that specifically sells plus-size gothic shoes for women, though. Usually I just browse around until I find a pair I like that's being sold in a 12 or 11 1/5, but it'd probably be next to impossible to find a 15 that way.
Sorry I can't help more.
