I have a '92 Convertible 5.0 and it has white leather seats/interior.I got lucky though,one of the reasons I bought it was the extreme mint conditons of the interior + seats.I doubt i'd see another Mustang with leather seats in this condition.They are usually tore up or all wrinkled.I wouldn't bother looking in a junk yard.The seats there will most likely be wrecked from sun damage or the rest of the elements.
I'm not sure how much they cost to re-skin them.Keep this post TTT and you should get moe info.