The ball bearings lasted for years...but your truck may have been worst on them than others. That said I'd give NAPA a try and if no success then go to a tractor trailer shop and ask to see the service man and find out who supplies them.
....if, and that is a big IF, you can get someone that knows a lot, or works, at a Timken Roller bearing place/supplier you may get lucky. I did that a few years ago with an odd bearing.
