Can anyone please tell me where I can get a new leather or rubber pulley for my treadle? I have had this leather one on it for so long that I don't remember where I purchased it.

if you mean the 'cord' between the flywheel and the machine, i bought mine at a sewing machine store. i had to ask for it, they keep theirs in the back.

That thingie is called a belt and you can get them at sewing repair shops.