I don't see why oem Kirby bearings are needed. You could just buy from a reputable bearing manufacturer (which no doubt is what Kirby does). Whatever bearing you need, just measure it and use McMaster to find the 'trade number' - like 608ZZ for example. That's a metric bearing, and the digits after the first 3 change sometimes, they indicate whether it's sealed, open, or shielded, or sometimes a combo of two. Then google or ebay your trade number and just pick one from a known brand like SKF or Timken or Koyo. For example, google "608 ball bearing."
I mean, I've been buying Chinesium 'skate board' bearings from thebigbearingstore.com, so far, so good. It isn't the 1980s anymore - when you bought Chinese brake rotors and had to have them turned on a lathe again to make them straight lol.