Not sure about Manufacturer's being "required" to provide replacement parts for 10 years. It's just good business sense for the manufacturer's to provide parts while they have lots of cars still on the road, which today people are keeping cars for 10 years, they have to for how much they pay for them. I just can't imagine how someone could require a manufacturer to do this, without it being unreasonably intrusive into the business, but government has done that.
There are a lot of complaints on this forum and others about spare parts being on back order for weeks even months, half a year. Since FIAT has taken over, and the company is now FCA, there is lot of business articles about FCA putting all its cash into new products and production. Its a pure guess, but perhaps FCA is ignoring the servicing of after sale vehicles and putting all their resources into making new vehicles. I don't know about other brands, I might be wrong and this might be an industry wide problem, not just FCA and it has something to do with the state of the economy.
Remember, the drivetrain and engines did NOT change much over the years. The drivetrain and engines are the same as the WK Grand Cherokee that was very popular.
I suspect the Dealer is blowing smoke up your butt, telling you have a classic and that is why they have trouble getting parts. The truth is likely they can't get parts for most of the vehicles being brought in, and they have to wait weeks for them on back order.