4 Track

I don't know about four, but the Zoom F4 has a 'poly' mode that will record 6 channels onto a single file (see page 23 of manual). Other than that you are looking at professional machines, most of which will do this. Personally I've never regarded it as much of an issue, as Audition will recombine two stereo files into an n-channel file (where n is anything you specify) very easily, and with sample accuracy.