Any MIDI interface box with a serial connection will work it is just hardware any Mac compatible sequencer will use. Check eBay, or your local music shop which may still have a few. As for Performer, I need to see if my copy can be duplicated in order to make an image as it seems to be extremely difficult to find these old copies. I got mine on eBay to go with a a vintage copy of Composer I've had since college. Set up a custom search on eBay for a year and just sit back and wait for it to alert you to a copy for sale.