The AD bearing dimensions are fairly oddball. I’ve looked into it. Best I can tell, the only available modern roller bearings were made for this very purpose.
You don’t necessarily “have to” source from specialty vendors. These were produced many decades ago, and NOS examples are on eBay. There is some cross over to other GM vehicles (I can’t remember if it’s inner, outer, or both), so these aren’t as scarce as one might assume.
