There is a "Sew Its For Sale yahoo group that you can join/register with and you could list it there. I was "looking for a machine" once and listed by "in search of" (not model specific, was just looking for a heavy duty machine and I received no less than 50 replies, the first one just mins after. Its not just machines, its patterns, books, fabrics, things related to sewing but a lot of machines.
Marysewfun