One place to get some 50/50 or 60/40 is the "local" radiator repair shop tank. It will require some cleaning, but will sure be the cheapest source of tin you will find!

Call several as some will NOT even talk to you about it others are quite friendly and cooperative!

Keep looking for good sources. Good sources for cheap lead ARE out there. I buy Wheel-Weights at a tire store nearby for 10 Cents per pound. I just bought 3,000+ pounds of pure linotype (still in the lines of type, not in ingot form) AND 250 pounds of 50% tin and 50% pure lead mixture, AND about 500 pounds of pure lead for 25 cents per pound.
I found that deal at a gun show. A guy had 1 ingot of lead with a post-it-note on it laying on his table. I asked him what type of lead it was and how much he wanted for it and how much he had. You can imagine my surprise!! Or rather my excitement.

Look close, look hard and you will find lead. I hope I never have to pay Midways prices, but it is a comfort to know it is there if I ever need it.
Follow the advice on hera, and call all of the local tire stores.

David