I bought one of these gearboxes at a swap meet which I really don't need, so I hope this is the one you are looking for. Since I'm one of those folks who still uses some geared setups, I'll hopefully use it some day if you don't want it, but wasn't thrilled that the seller wanted $10 firm. The gearbox and the drive gear appear to be new. They actually had 2, but I wasn't going to spend $20 for two of these, not knowing if you would want them or not. Wish I had your phone# when I was there.
Let me know if you want it for cost plus shipping which should be about $15.
edit: I questioned if it was the ratio that you needed as MA uses 3 different ratios, although 3:1 seems to be the most popular. A tri-motor setup wouldn't be bothered with the center motor on a different ratio, but you would want to match the wing gearboxes.
This is the club website: