You can get them anywhere - any auto parts stores, RockAuto, Parts Mike, ebay, Amazon, etc. I believe the part numbers can be universally cross referenced to National, SKF, Nachi, etc. I believe that the T18A and most of them use the "thin" 308L1 for the front input bearing. May need to confirm though once you have the old one out.
308L1 - 20MM "Thin" version
6308N - 23 mm "Thick" version