I have a vintage 20 gauge Lee loader. I would like to load brass shells with smokeless powder and felt wads, paper seals and such.
Is there a good source for.load data?

Not really. There are ways to get it done, but if you wanted tested loads your only option is to make them and send them off for testing. I only know one person that will test them. His mane is Bruce Ducksworth out of GA.