Anyone know any sources of good waifu erotic literature?
I doubt you'll find translations of Japanese fanfics (or of fanfics in general) anywhere, so they'd probably have to be English-language originals. As much as it irks me to suggest it, fanfiction.net is probably your best bet.
ASSTR.org does not have such stories, and that's all sites for literotica that I know.
Good luck in your search.
Written Erotic Literature can be good too.
Just give the written word a chance...