He doesn't own his files. They are YOUR files. The practice may charge you a nominal fee ($25) for "copying" the files to give to you.
When you asked if you could see another DR I assume you meant that you'd like to see another DR in the same GI practice as the one you're currently seeing. That should be possible, too, and simply requires that you call the main reception area and ask to have an appointment with another GI. Inside their medical practice they may frown upon DRs taking patients away from others, but given the schedule conflict you've identified I would think everyone could agree to a new arrangement. If they can't however, you are free to take your business wherever you want.
Oh, and it's not important why he only sees patients on Tuesdays. You don't know anything about his personal life I'd bet, so please don't make assumptions about him. My GI, for example, is in his mid-60s and had a major heart attack a few years ago. He completely changed the way he practices medicine and now has a much smaller office and takes fewer patients. What's important is what works for you, and if Tuesday isn't going to work for you then find someone who can see you on other days of the week.