Ebay, loads of vinyl on there, search vinyl fabric, all the colours under the sun.
And in all seriousness my tiger print cover is referred to as ponyskin, there's other types out there, there's a little noticeable wear on mine where I've been sat, but it's done about 10,000 miles and cost about £4/5 for the material for the seat.
With mine I left the original vinyl on and just recovered that, keeps the sponge dry!