The koss drivers are encapsulated in a plastic shell for tunning which is hard to break without damaging the speaker. If you really want the KSC75 sound the best solution would be to buy them and just make your own casing. Or you can try this...

I was thinking about headbands, somebody had a good experience with sub-20USD headphones which could be used as donors? I like the look of superlux HD330 as they look Beyerdynamic compatible (I can't buy spare parts from them, they don't ship to me).