I've pretty much been able to find any part I've needed on ebay or Bonanza...even hard-to-find, obscure parts. If they're not listed today, it seems that they will be within a couple weeks.
Up until a couple years ago, there was a great old Singer shop near here. It had been in business for over 50 years & he repaired all brands.They had any part for any brand of machine that you could imagine....& a huge room full of parts machines. I'd bring tools & he'd just turn me loose in the place! He never charged over $1-$2 a part. Well, he retired & a lady nearby bought out the shop. Prices are WAY up & she didn't keep much that wasn't Singer.