Actually I'm just learning as I go. When it comes to small parts I go to my local sewing machine guy and he "usually" has what I want.
You can go to Singer at: {
http://www.singerco.com/support/replacement-parts-chart } and download the .pdf parts list for your machine. Print it, then take that with your machine to your local Singer shop if there is one, or call the Singer fix it shops as listed in the boxes on the same page. Perhaps they will have it.
I'd hate to see a decent machine sold for parts just because of one screw and some dufas salesman that didn't want to work on it. The 70s Singers were still mostly metal and most of them sewed quite well.
Joe