I have had the best luck with the unexpected surprises at garage sales. I ask do you have any old machines. My last score was a FW for $75 doing this. People often do not think to put them out or with the elderly they do not think anyone wants them. I also leave my little biz card at the flea markets with the owner or manager. They pass the word along that I collect old machines. And I placed an ad earlier this summer on CL that I would pick up old machines. Got several that were junk, but was able to salvage the drawers out of a treadle that was falling apart, repair a 60's singer and gave it to the teenage neighbor girl who wants to learn to sew AND scored a 185K, my fav color green.
Just put the word out and you will find them