[redshift]

Avidrc.com has the 12 x 16, and 6 x 13 x 5, 1 buck each. You can run standard 6 x 12 x 4's with the reducer sleeve, I have no idea why Traxxas did that, 6 x 13 is not a standard size. You can try Amain, Acer and vxb.com also if you need more options.

While you are waiting for your new bearings, try this- take a sharp X acto blade and gently get under the edge of the seals on your bad bearings and pry them up. Blast them out with a high solvent and turn them a few times until the debris is clear, I use oil instead of grease, anything between 30 and 90 weight should be fine. Once you do a few they are easy, and in a pinch you'll be able to run them when you can't wait for replacements.