I don't think I have ever heard of anyone repopping benchseat foam. The same goes for rear seats. You just have to take these to an upholster or do it yourself.
Legendary Auto Interiors sells it, along with all of the other items that you will need to rebuild your seats. I used it on the front and rear seats when we restored my son's 72 Dart Swinger's interior and I will use it on my rear seat in my 66 Coronet 500 when I start it's interior restoration soon. It's a very high quality closed cell foam and I've been very happy with it. It's 2" thick and you can buy it in various lengths.
Richard
www.legendaryautointeriors.com
1-800-363-8804