I have found that during this area of design its far from a case of putting a cover over a seat, The interiors became very complex and difficult for the lay man to fit. By the time the material is shot most of the dunlopillow rubber base material and coil springs are disintegrating from 60 years of use and needing someone in the trade to complete these types of jobs,
Many are hog ringed through the seats to secure them and owners would not have the tools. What I'm trying to say is if if kits are available one would probably need a trimmer to fit them and and make other repairs, if that's the case its probably more economic to buy the cloth and have him make it. Good luck in your search.