I do not think you will find a locking rear for a 3rd gen in country. I expect you will need to go overseas for that.
The spline count in a 3rd gen is different than in the 2nd, I have not measured the width of the carrier to see if they are the same. If they are close you maybe able to respline your inner stub axles and use the earlier diff. But I do not know the diameter of the 33 spline stubs to be sure this can be done.
The front should use the same diff sections as a 2nd gen so an ARB should be available.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.