These shops are likely correct. To double check, look at a website like crutchfield.com. They have every known radio along with installation recommendations. I contacted them about 2 years ago regarding my 2004 Quest radio that would lose power intermittently (common issue) and there were no aftermarket radios. I found a dealer who sold re-furbished Nissan radio on E-Bay (there were several dealers). That has worked for the past 15 months.
I would try E-Bay for a re-furbished unit. A factory unit will cost you about $1000.