Searching flea-pay and C-list is one way. Ask around about old salvage yards but they may be as rare as those transmissions in the midwest and northeast. Flat top Bob Owen's salvage yard up in the panhandle (Wellington, Tx) and a yard over in Seguin named John's Salvage would be worth a call but shipping to Elmira-Horseheads may be pretty high. I used to ship and receive a lot of helicopter stuff from the old Schweizer Aircraft Plant up there.
What parts are damaged on your 2-speed? The reason I ask is that there is a good chance that the only thing different about the two V8 transmissions is the main case. All the other parts are more than likely the same, The ones for the little 6-cylinder engines still had an air cooling feature for the torque converter but the V8 types were all liquid cooled set ups. I'm not sure if the early ones were vacuum modulated but all 1961 & later types were.
Other than having a front and rear pump, these units were pretty simple. There are even U-tube videos on them out there. Two bands, a clutch pack, and a simple planetary is what makes them shift & go. Even the valve body and regulator are relatively simple. I wished I'd learned on something that simple before tackling the Cruise-O-Matic in an old 64 T-bird I used to have.