Tul is said to know all things about the nature of soulmates and from my experience, can draw in the nearest match for you.
I tend to look at the term soul mate much more loosely than the rest of the forum, as in I think it’s a match for you, not necessarily one you have a past life history with, however.
Believe he can be found in Kingdom of Flames, but his sigil is floating around here on the forum in a few threads. I’ve personally evoked him like you would any other demon.