There is a thread over on Teamshelby.com that has the Timken part numbers. From what I heard, they weren't available, though at least 2 members there had been able to get one (I think AFTER bed things happen).
The original pinion bearing was actually easy to save in pristine condition (Well at least as far as I know after only 30 miles!)
Harbor Freight sells a tool kit for $50 that has the bearing splitter you'll need to remove it (Thanks to SVTBird I think for that GREAT tip!). We needed some longer threaded rods to get it to work though, but happend to have some on hand.
TD