Hi there,
I did check on the yellow pages and found this company near you
Plastics Warehouse Plastics – Manufacturers & Supplies
Tel: 01983 405269| 6a, Lake Industrial Way, Sandown, Isle of Wight PO36 9PL
I normaly go to a local plastics dealer and get it there it is alot cheaper than a modelshop
I can’t remember what it is the trade name is but
for a 5Ft x 2Ft sheet you can pay about £6 to £8
hope this helps