There was no factory option for leather in Gen. I Monteros (hence Raiders)in North America.

Any leather you find in a Gen I is from an aftermarket kit that was available at the time. I've seen one and it was highly...uh...OK. But, that was due maily to the half-assed installation job.

As stated, the best bet is to have your current seats recovered in leather or get some leather Starion seats and mod to fit.

87 Montero, bought new, by me -
88/89 intercooled Starion Turbo engine-
with awesome audio.