Rio Grande Jewelry Supply
The Pewterers guild normally keeps the following types of pewter on hand, both purchased from Rio Grande:
Aqua Clean Casting Metal
High strength metal, does not fill out detail particularly well but works well for many moulds. Harder to bend.
Lead-Free Tin Alloy Casting Metal
Great for details, very soft and easy to cast but not particularly strong. Useful for pieces with pin-backs that need to bend easily, or for tokens that don't need to be very strong.
They sell catalog number 750031 (92% Tin, 7.5% Antimony, .5% Copper)
They sell nominal 5.5# bars, and you can order as little as 1 bar. Their prices are typically high, but they don't change them very often. So if tin prices skyrocket, their (old un-raised) prices seem more reasonable for a while. But, if they raise their price before the price drops, then their prices can seem astronomical in comparison to others. They offer price breaks at 10 bars (55#) and at 20 bars (110#.).