The vehicle wasn't discontinued, but the 1PZ engine was. I'm not sure if the engine is that poor or if there is a defect in its design. It may just be that Toyota decided it no longer fit their engine needs. It is possible that they want to streamline their product lines to reduce dealer parts inventory, etc. Or they find in the markets they are, the fuel savings do not justify the smaller engine.
The 1HZ has replaced the 1PZ in all their heavy duty 7 series. As far as I know the 1PZ was only used in their J7 land cruisers and was never used in other vehicle lines, where as the 1HZ was used in the J8 land cruisers and Coaster buses during the same period. Maybe because the number of 1PZ engines needed was relatively small Toyota decided to stop it?
To give you some ideas what aid organizations carry to far away places, this is what Toyota of Gibraltar recommends for the first 2 years or 40,000 kms:
spares list
and what they recommend in general:
"essential items that can replace broken or damaged parts which could lead to a vehicle breakdown"
Dave