My local ACE Hardware store had a smallish box in the "welding" section with an assortment of replacement lens. I bought the 50mm? rounds - set of 2 for about $1.50. Note you MUST use a separate pane of glass for the flash and the shutter.
I say "welding" section as they really didn't have a welding department, only a small isle of common replacement parts.
(Edited by Matt in MO at 8:04 am on July 23, 2001)
Way to go Matt! My wife works for Ace Hardware. She got mine for me (employee discount so I won't tell you the price! ). I got the big square lense (6"x6" I think) and cut small squares to cover the flash, shutter, emitter, and frame counter holes.