Replacement Transmission

[Periodic31]

I have a 1931 Imperial with a 4 speed transmission (new in 1931). Several people have identified that this can be replaced with a 3 speed from a Desoto or a Dodge. I have no problem with the weird shift pattern (people say it is hard to get used to it) or the fact that gear one and two are straight teeth and 3 and 4 are rounded; but I would like to find a possible 3 speed replacement to store just in case. Any help in identifying/locating one would be much appreciated. Thank you Gentlemen!!