You should be able to get them from your dealer, but they're pretty expensive via that channel. Look in the FAQ to find the Alpine unit model number and see if you can buy the Alpine cartridge from the usual car stereo discounters. Also, if availability is a problem, the old 95 BMW M3s used the same type of changer/cartridge so you can get the BMW equivalent from the usual BMW aftermarket suppliers, except that they'll be marked "BMW."