Just finished restoring a Buffalo Forge Blower with the same problem, the caged thrust bearings on the lower shaft were just pile of rust. I tried every bearing shop in the are without luck. I ended up replacing all the ball bearings with new 5 mm ( I think they were actually 5.1 mm) ball bearings that I took out of casters from TSC. Since I didn't have them caged, I surrounded the shaft with more bearings than were originally there, greased the heck outta them and added a thin brass washer to hold them in on the fan side. The blower works great now.