I would join vintage sewing machine groups on Yahoo. There is a group for vintage Singers, another for vintage Kenmores (I think), etc. Plus there is a group called wefixit whose interest is in fixing up old sewing machines of any brand.
Some of the problems you mention (such as the bobbin winding on the last one) sound like relatively simple fixes. There are places online to order a replacement foot pedal, etc. The Yahoo groups are likely to be able to point you in the right direction.
If all else fails, you can take a non-working machine to Goodwill or a thrift shop. If the defect is not obvious, put a strip of painter's tape on the machine with "parts only" on it, or a description of the problem.