This thread will provide a place to list sources for parts and information on repairing vintage machines, and how to search for information on the Internet.
Please note that this isn't somewhere to advertise or exchange parts or machines and this would be a breach of QB rules.
As a start, if you have a 201, model 15, 66 or 99 you should check out the tfsr (tools for self reliance) website for their repair manual series.
ISMACS is the sewing machine collectors society. They have a lot of information about sewing machines, mainly Singers. If you need to look up a serial number or a model number, it is a very useful resource.