Since Montero Sports are very limited on mods, it is no surprise that there is a limited selection of lockers for them. If anyone knows of any others, please post up. Welding it is not an option.

ARB Air Front Locker is available for all models:
Challenger/Montero Sport Front IFS, 28 spline with a shaft diameter of 28.8 (1.13") is the RD110.

ARB Air Rear Locker is only available for the 3.0 Liter models:
The Montero Sport Rear 3.0L V6, 9.00" RG 2 (Large Differential has a crown wheel spigot diameter of 145mm) has a shaft diameter of 30.5 (1.20") 28 Spline is the RD25.
www.arbusa.com

Eaton Posi Locker:
MIT/P4 4.62 Gears 24 Spline. All I can figure on this one, is that it is for an older one, because the spline count does not match the ARB application's spline count.
http://www.reiderracing.com/eatonposi.htm

This is it, it's all I have found.