My go-to is pintrest! there's lots of stuff, try searching like "[goth/alt] diy" and you're bound to get loads of results! I'd even try youtube, there's probably a few goths on there, even if they're older videos, i'm sure that'd be a good thing!
if you really can't seem to find anything i'd suggest just taking a peek at some finished outfits and seeing if there's anything you might be ale to replicate, I was able to repurpose a few pieces of clothing this way