Hello my friend! I am answering this because I've had the same question a few years back! So, the first place to go is pixiv.com! There you can search for guro categories by typing tags and even doing a search with multipe tags.Tips&tricks here: after you type a word like necro or necrophilia wait a few seconds and the japanese word or words for it will appear in the hidden list below, select one and will have infinitely more results than with the english tag.The second option is dlsite.com/maniax using the advanced search there should get you a fair share of work containing guro, the other places to search are getchu.com hitomi.la exhentai(best for western guro) It's enough to follow a lead then find the artist or artists you like and then do research about them.Indeed today's scene requires some work and I can give you all the tips&tricks here because I'll have to fill pages on searching these sites and the japanese web. I've given you just enough info and a basis for your own research.And you will find many gems.For example here is something I've found on dlsite using the keywords(mother, shota, torture, fiendish/brutal):
https://www.dlsite.com/maniax/work/=/product_id/RJ317121.html
HF!^^