For seat material we have used Premier Contract Fabrics of Peebles EH45 8ER tel 01721 724310. They are a major supplier of fully certified/burn tested fabrics. Although potentially expensive, as long as you don't mind the colour you might get an off-cut; I assume you don't need more than 2 seats' worth. For cushions we have used Airline Services of Manchester 0161 489 3173, again a big firm but may be able to put you onto a foam supplier. No contacts for panels I'm afraid.