The bearings are made by very few, sold by many. The ones I'd choose are National, SKF, and Timken. I'd pick Timken although it;s hard to say if there is any difference one could notice. Rockauto.com has them for less than $30. No way the clutch manufacturers build their own bearings, that's an entirely different realm of manufacturing. You can also buy just the bearing, less the cast iron carrier, for around $15.00.
R.