The 400. 500 an 600 series cams are the same as I understand it. I just bought a big assortment of cams on ebay and they should arrive in a couple of days. I have the original 5 for the 503 and am looking to fill in the other 20. Ill let you know when they get here if they are the same.
I dont think the ones from the Touch and Sew are the same, but they are in this assortment too. So, I can check it all out when they arrive. If they are the same, I can probably hook you up with some of the duplicates.
The 300 series cams are deffinately different. They are flat, not the top hat kind the later series take.
Hang tight, it should just be a couple of days.