I used to buy from ebay, I found a really good shop there, but have also found suppliers through machine knitting magazines, I like Metropolitan Machine Knitting. It is a British company and I am sure you would like to find somewhere closer to home, there are often lists of stockists on machine knitting sites. Punchcards are generally either twenty four or sixty stitches wide, I think they will fit any make of machine, given the same guage.
