I had the shells for the sprockets made at my friend's welding shop for about $1 a piece. He had some tooling that was really close to the correct shape for the shell in his press. The conservation directives in the members library will give the dimensions for the size of the plate to form. If you have access to a shop press you could make some sort of crude die to form them yourself. I was able to hand form the "prototype" that I took to the shop so thats an option. I've also read that some fellas used the correct size pipe cut in half with good results. I would steer clear of trying to just welding the sprockets up, that would be a lot of welding

Here's the sprockets after welding 

www.manta.com/c/mmdjxfq/pigeon-products-mfg

sprocket liners

Awesome, thanks for the information!

Nice pictures.
I don't think I have ever seen a sprocket that has no previous welding on it.
Most have had new sprockets welding on.

Thanks! It's a fairly solid machine all around. Most of the prior owners did little to no maintenance to it. I've already done a lot of work to it & want to catch what I can before it becomes too much of an issue.