I have a pair of Sony MDR-CD7 headphones, but unlike the CD6, the replacement pads are still available from Partsolver http://www.partsolver.com/ for USD11.71 each.
I have been very pleased with the headphones but since purchasing them in 1990 I am now up for my 3rd set of pads and have now clocked up the original cost of the headphones themselves just in replacement pads. Quite frankly I cannot see how a piece of foam plastic covered with a black simulated leather coating can cost so much, particularly as they last only a few years even while sitting in a drawer. Surely the plastic coating should not perish just sitting around. The foam base material itself doesn't deteriorate, just the black coating.
I am thinking of having a go at covering the foam in some thin stretch material and using double sided tape to stick them on the earphones rather than buy genuine pads at an exorbitant price which I know will deteriorate in a few years.