As you have probably seen/know, you can buy new leather covers and foam from the US, including covers already mounted on the foam, but its expensive. Look on the web at Ecklers, MidAmerica etc. Keith at Eurovettes could help you on that. Used to be able to get "faux" and "drivers quality leather" which was cheaper.
Might be cheaper to just buy the foam, and get them covered over here, with what might be better quality leather anyway? Does anyone know, is there any way you can treat old seat foam to pump it back up to its original shape/strength?