Under carpet foam

[sevans]

After spending the last week trying to source some under carpet foam I can't believe it's so difficult to obtain the right stuff. After speaking to a few people I think it's known as 10 or 12 lb reconstituted foam. The 10 or 12 lb relates to the density. The most I could find was 6 lb and this does not seem dense enough to provide adequate sound and vibration deadening
Does anyone know where this can be obtained or suggest an alternative
Thanks.