I found a vendor with a massive catalog that seems to contain every spring known to man
The price was a little high, but since I;m not ordering 1000 at a time, I'm happy. I'm honestly surprised they sold me just 3 to start with (I ordered a total of 9 so I could try a couple different sizes and part numbers)
I've got a local shop that I'm going to try for the balls on Monday. I shot one across the garage the other night, so I now have a vested interest in finding some.