Paul Barnhart, Barnhart Studios, carries a good selection of tinplate, and a lot of other needed supplies.
As for the tools, good luck. I got a few of mine on Ebay before the prices went through the roof. They do not show up in the flea markets around here, but there are some guys online that sell used metalworking machinery. They are not cheap, but better than fighting it out on ebay usually.
The thing that I am learning from books, advise and experience is that a lot of tinsmithing can be done over pieces of pipe, wooden blocks and various found objects. The stakes are great, but not absolutely necessary to get started.