I met my wife on a dating site.
We both have mental health issues. Neither one of us included anything about this on our profiles, but we did bring it up (not immediately) but pretty early in our relationship. It worked out great. I realize this is not the usual, and won't happen for everyone. But I just wanted to say that you can still find someone with mental illness. We did.
You'll have to plow through a lot of wrong people on any dating site, but I think its worth it to take the chance.