Good luck finding an aftermarket unit to fit. The radio on our 2004 Quest will shutoff when put into gear. It only happens intermittently. There is a TSB (not a recall) for this issue that calls for replacing the radio unit. I searched Crutchfield as well and got the same result. I figure if Crutchfield does not have a unit that is compatible with the Quest, it probably doesn’t exist.
The original unit is made by Clarion and replacing it seems pretty easy. I’m not sure if Clarion will sell directly to the consumer though. I searched the internet several months ago and found a couple sites that sell refurbished units. Unfortunately, I can’t remember the sites. I do remember the prices were in the mid $300s.