Hi Por,
Just an idea since you might not be able to find an OEM replacement, but you might go to a used car lot, take a look at car seats of 1 to 5 year old models (probably European models), and find one that has seats nearly the same size as the crossfires (take the measurements with you). Order the foam for that model, and then with a few cuts, you can make the foam fit your upholstery - it's very forgiving. Or you buy a very thick square of foam and hot knife it into shape. (Again, the foam doesn't have to match exactly since it will compress into shape.)
-Jerry