Are you strictly dating vegans? Maybe you are open to dating vegetarians? Maybe you view it as a personal choice and you don’t mind dating non-vegans?
Does the goal of the relationship change your answer? If it is a long-term relationship, or a short-term one, or a casual one, or friends-with-benifitis or even a one-night-stand?
If you find places where those people hang out, you’ll do a lot better.
Fortunately where I live the queer spaces, anarchist spaces, and vegan spaces feature heavy overlap. So it’s not as hard as it might seem. (Still a very small pool though!)
Yeah, that’s actually how I met my last partner. We met at a vegan rally