Finding a car with a shot transmission and doing the swap thing is the way to go, IMHO. Two years ago my employer contemplated transfering me to the USA and I enquired about the importation of my one year old canadian-spec vehicle to the US. That proved to be such a monumental pain in the A$$ that I quickly abandoned the idea and negotiated an alternate plan with my company (at the end of the day the transfer did not happen).
On a more technical note, you are probably well aware that the final drive ratio for an automatic typically differs from the manual version. Nevertheless, a rear end from a similar US model could do the trick. For example, there is specific final drive info on the 86-93 w124 series.
300E auto - 2.87:1 / 300E 5-speed - 3.07:1
Potential rear-end donors are 260E auto and 300E 4-matic auto - both have 3.07:1.