Sew-Classic.com will probably either have the needed parts or tell you who may have them. That is a beautiful, tiger oak, 3/4 sawn cabinet. Thank you for saving her from one less thoughtful. This is a real treasure. Joe, our resident machine doctor, may have some words of wisdom for you also. Also,
http://www.ismacs.net/singer_sewing_...sses-1-99.html, the only link I have for them, may be helpful. Ismacs will have downloadable versions of most manuals.
I paid for one, then found it there for free. Belts will be at Sew-Classic.com as well as most parts for vintage machine.
Ebay is also a source for parts, but buyer beware. Good luck and long life to both of you.