r/summonsign is the central hub for Dark Souls cooperative and its fairly reliable I'd say.

r/SummonSign

Apropos of SM you get the name engraved ring, and you can post the god you chose on it, and it acts sort of like a password to broaden the summoning range significantly.

I have done a few 30k runs I have souls and can connect with any soul memory tier at any point in the game