israelk: thanks for the reply. Permanent magnet or spring-applied failsafe brakes are pretty standard things. Very common on robot arms that have maintain their position even if the power fails - think "parking brake".
There are many manufacturers of larger sizes, but I'm on the hunt for a small one, which are much less common. Examples can be found in an old Puma-260, but there are no vendor markings. The only source I have found is the old Vernitron line now being built by Island Components.
MikeHalloran: I'm looking for a handful of prototypes right now, but am ultimately looking for a ISO supplier for volume production of 1000's of units for a surgical robot. Do you have any leads?
Alternatively, I'm considering designing the unit myself if I have to, in order to get the size I require.
Thanks!
-Bruce