I'm not the biggest Reddit fan, but the Reddit userbase is probably the place where we can find the most of people who could be interested in Lemmy. Text-based forums aren't that popular nowadays, and Reddit is by fart the largest.

About a specific approach, there was also this post: https://old.reddit.com/r/BoycottUnitedStates/comments/1jrcrh6/lemmy_as_an_nonus_alternative_to_red_dit_using/

Had both a one-liner and a bunch of countries instances.