I presume you want to replace the entire carpet throughout the floor pan? If so there's a company on the quays (I hope they're still there) called CUC (Car Upholstery Company I think) who do all that sort of stuff- carpet, headlining, leatherette, trims and fastenings. The old carpet can be used to make a template, reverse the new carpet, lay your old one face down and trace around with a biro or (orange) marking pencil and cut away. I done this in the past with older cars, depends on the complexity of the floor pan shape though.