I have one of these and it's my favorite vintage machine! They're nicknamed "Rocketeer".
These are slant-shank machines, so the feet are slightly unique. But Singer made slant-shanks for awhile and the feet are still being made and are available online. Just hunt for "slant shank". Singer made buttonholers for slant-shank too, they come in a pink oval case; I see them periodically at thrift shops for around ten bucks.
There's the 500A and the 503A that look very similar and both are called "Rocketeer" - main difference is that the 500 has more built-in stitches. Both take cams; the cams are also pretty easy to find as they're the same style Singer used for a few different models.
New power cords/pedals are easy to find online still too. I don't like the button-style pedal that mine came with so I bought a modern clamshell style one to use for myself; I think I paid about $25 for it.
Manuals are a little harder to find but if you keep your eyes on eBay they do turn up. I think you can buy photocopied versions on CD pretty easily. (I waited to find an original paper one, but I DID find one!)
They take class 66 bobbins - modern Singer-brand class 66 bobbins will NOT fit, however. They are made much cheaper now and have flaws. If you need bobbins, don't buy them somewhere like Joann's, buy them somewhere like Sew Classic, or look for vintage bobbins on eBay.
Happy hunting! I LOOOOVE my Rocketeer, it's a great machine.