The best canvas seat covers out there for Land Cruisers and Land Rovers are both from SA: Mellville & Moon and Escape. Both very high quality products. But neither are being imported to US. Special order (after Rand exchnge rate) is >$800 bux just for fronts. (Equipt does stock Escape covers for FZJ80 but not for UZJ100)
However, Kexby may be an option.
http://www.kexbylimited.com/stocked-products/land-rover/range-rover-classic-seat-covers/
Tony, the owner of Kexby, did a run of covers for RRCs and I bought a set. VERY high quality, on par with the SA products, but made here in the US. Front covers had multi tool, radio, and map pockets sewn in, and were 300 bux for a pair.
That said, Kexby is not producing covers for UZJ100s.....yet....
Tony owns a UZJ100 and patterning a set is on his "to do" list. Like most small businessmen, if he gets enough interest no doubt it will move up on the list. If a few interested people post up in this thread I'll link him to it.