They come up on Ebay pretty often- - - -usually the BIG ones that were used on heavy trucks. Be aware they use non-synchronized gearing, so shifting one on the fly can be a challenge. I learned to drive trucks on a B-73 Mack with a 5 X 3 transmission setup, and after a while I could run all 15 gears without using the clutch except to start and stop. If you're considering using a Brownie in a truck smaller than about a 2 ton, you'll have a big problem adapting the driveline yokes to the small U joints smaller trucks use- - - -custom made drivelines to both ends of the Brownie.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!