In addition to all already mentioned for suicide
www.hermantheshocker.com
And for cutting
This is a site where you won't be judged or shamed. Safety & harm reduction is encouraged here
selfharm.pics
https://www.psyke.org/ (super oldschool)
Reddit is currently on a cruisade against suicide/self-harm content (r/eyeblech got banned like a week ago) but there is:
r/NSFL__/
r/CrimeScene/
r/MorbidReality/
r/MostShocking/
Like 10 different cutting subreddits at a time that will get banned the instant they get reported once.
And as said previously there is a whole community for selfharm on twitter called shtwt, should be easily enough to find accounts just by searching that and any related tags you see.
I would personally say that watchpeopledie.tv is currently the best resource though for this type of suicide/gore content . Although it is mostly reposts nowadays it has a great archive if you haven't saw much suicide/gore type content before.