Loosescrews sells loose bearings for a good price. I bought some grade 25 from them, as I didn't want to bother the machine shop here at work.

I'm guessing you need 50 5/32" for the headset, 25 top and bottom?

I also got 3/16" for the front and rear hub, and 1/4" for the bootom bracket.

You could also go to a local industial supplier or bearing company and get what you need. Hardware stores may also have some, but can get expensive fast.