Jim, I'm sorry to say that the chances of finding a transaxle for a 12/40 are basically zero. There are only two cars known to survive (and I'm assuming you now have one of these). The usual gearbox/axle for the 4-cyl, 12hp cars is rare enough but the Sports model has different gear ratios right the way through the box (3.8, 7, 14 with reverse 19, whereas standard 4-cyl are 4.5, 8.2, 16.2 and 22.1) The worm and wheel, plus the gears, may all be different. I fear this means cutting new gears, and worm and wheel, all dependent on the damage that requires a substitute transaxle.
Now, saying that, the positive side is that a rebuild is possible - that can be done, using the right companies plus, of course, some parts will be salvageable......so, all is not lost!