For seats and such items I'd look for salvage vehicles to buy the items you want from. Many of the items are also still availible from Land Rover and sources like our host. I'm sure some RR owners with chime in with their favorite sources. You could also check with dealers that often sell these to see where they get there parts. One place I can think of is Red Mountain Rovers in Birmingham,Al. I don't know them and have no association-blah,blah...but they alwasy have several of these for sale so they must have to get parts to service them and the fix them up for sale.
64 IIa 88
94 Discovery
06 Toyota 4R (DD)
~Matt
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"Not all who wander are lost"~Tolkein