I get carpet from stock interiors. They have an ebay store as well and it's about $135.00 with free shipping and fits great, well worth the money, even has the foot pad under the pedals.
I do use regular carpeting in my 73 station wagon, but only in the cargo area since it's not reproduced that I know of. So far so good, even though it doesn't match the passenger area or the interior color, but it is a brownish color. I am in the process of making a vinyl cargo cover that will go from the back of the rear seat to the tail gate to cover up the rear area and still look somewhat like a "Pinto option" thing, even though it wasn't.