There are lots of options, but mainly changes on the theme. The tranny in the 12g and 10 tractors is a very common peerless unit, and while not limitless, the parts are still out there.
Peerless 2300 Series transaxle. You can find it in John Deere 110, 112, 210, 212, 214, can find them in many of the Massey Ferguson GTs, also used in 1970s Gilson GTs (made for Montgomery Wards). Also can find a no reverse version of the 2300 in Elec Traks. My Springfield / Toro tractors use the 2300 in a couple of the models, but it's so hard to find them I don't want anyone taking those for other brands, as the input shaft is opposite most other brands, and the housings are unique, and I have a hard enough time finding whole tractors... So parts are more more important for me to obtain whenever I see them.
If you need parts for Peerless 2300, Pm 'Superaben' (Ben W. / Old Paths Equipment) as he sells a Peerless 2300 series rebuild kit, and any other parts you might need. If he doesn't have it, he can help you find it.