The OP asked, "Is There A Ready Source For Tin?". The answer, THERE SURE IS!
When you are "ready" get on your horse and head to the Thrift Store, the Bargain Barn, Resale Shop, 2nd Hand Store, Flea Market, and Garage Sale in your neighborhood and your neighbor's neighborhood as the "source" of a heap of cheap and quite often available pewter...but you have GOT to work for it.
Every time I am out and about I try to go through a different area. Knowing where I have been in the last 30-days helps, by not going back to the same places too often, as their stock does not turn over nearly that fast. Bargain, negotiate, finagle, and haggle over price of pieces that may, or may not, reach one pound.
The latest score was Saturday in a consignment ANTIQUE SHOP where price is expected to be HIGH. The $6 asking price was negotiated to $4. The candle holder, labeled on the bottom as 95% tin, was 1.25 pounds by scale when I got home. Not too shabby as that will turn 62.5 pounds of lead into ~2800 x 158 grain x 357 Mag. SWC's of 49/49/2 percent - Pb/WW/Sn!