ISMACS is a good place to start looking for information. Website is
http://www.ismacs.net/faq.html
Your machine looks like a Singer model 66 to me. It is pretty easy to purchase a replacement bobbin case for it, and the bobbins are widely available in places like JoAnn's.
There are also groups you can join that discuss vintage Singer sewing machines. vintagesingers and Singer are two groups you can join at
http://groups.yahoo.com
Oops! I just took a closer look at your pictures, and that is a drop-in bobbin. You are not missing the bobbin case, and I think that rules out a model 66. By jammed, do you mean that you cannot rotate the wheel fully?