Originally Posted by the royal 'we'
(Harris Cyclery has some available for $20, pn. FW8946.)
I don't think those are uniglide compatable. It say's it's STX-RC which means no threads and it says it's 11 tooth compatible.
You're going to have to make sure your's is 7 speed compatible or you will be looking for a used 7 speed uniglide freehub. I recommend updating to the hyperglide freehub (the one suggested above) and a new 7 speed HG cassette.
1 Super Record bike, 1 Nuovo Record bike, 1 Pista, 1 Road, 1 Cyclocross/Allrounder, 1 MTB, 1 Touring, 1 Fixed gear