When I did the seat for my '63 I got new foam from a local upholstery place. Many of them will sell sheets of foam, just shape it yourself. One word of warning... it's not cheap. The total bill just for the foam for my bench seat was right at $150 and overall it cost me just over $300 to do the whole upholstery job myself. So, get some quotes and what you come up with for prices.
