The transmission in your Montero Sport is specific to that vehicle only. While there are parts here and there that cross over to other makes due to shared vendors, the transmission itself is not associated with Toyota.
What you are like thinking of is the ~85-89 Montero full size which used a Toyota A43 type transmission found in Toyota base pickups from the mid 90s.
Because your transmission is stuck in failsafe mode, it is important to find out -why- it is in this state rather than just rebuild the transmission. There are many different things that can cause th transmission to resort to fail safe that do not equate to an internal failure.
Unfortunately most scan tools are not going to be able to pull codes for the transmission. Ideally you need a Mitsubishi scanner MUTII or MUTIII to read these codes and identify the failure point (or the computers assumed failure point).
You can however read the codes manually with no scan tool.
To do this, you will need to locate the Diagnostic terminal under the driver side dash (where the scan tools hook up), and ground pin 1 of the terminal. Turn the key on and the N(eutral) light will flash the codes at you.
Once you determine the interpreted cause of the fail safe mode, then you can get started determining a course of action. It may end up that you do in fact need a transmission, but it also may end up that you just need a solenoid or speed sensor. The first step is to get those codes, and find a shop you can trust... preferably one that does not try to sell you a transmission without even knowing what is wrong with your vehicle.
Let me know if you need any further assistance.