I vote for Cecilia's answer.
I would say craigslist. There is a local sewing shop here(ish) that isn't just quilting. They do random upcycling and and vintage patterns and the like and as far as I know, they don't have a machine brand they sell. I have considered offering them a consignment deal on cleaned up machines. Or maybe they have a bulletin board or something.
I'm just thinking out loud, obviously.