Without looking at yours,....I'd say 1/4 " pressed board from a home improvement center, a can of spray glue, (same place),.....and stop off on your way home at your hometowns big fabric retailer and dig through their bolts of vinyl.
All you need is a jump-up-and-down saw and a pair of you wifes good scissors.
You might go through the phone book and go to the nearest "Upholstery Supply".
They usually have a beautiful selection! Pretty cheap too!