I don't think they could just swap barrels and make everything right either. Don't barrels have SN scribed on the lug? They could swap guns to make it right, it would just require some paperwork be done. Next time maybe they'll have their gunsmith check things a little more closely.
Swapping the entire gun is NOT an option at all, In 99% of the situations it's simply not possible. The gun is considered used, the only other option is for the dealer to assume all fees and return it to the manufacturer for the customer. BUT the customer is left with no money AND no product. NOT the best situation. This is why I would check fit of a different barrel and with luck I would be able to have a satisfied customer, with a shoot able firearm he paid good money for.
Yes the last couple digits are on the lug, but as I mentioned that is something I (as the selling dealer) would work out with whom ever I needed to. All in an effort to make good for my customer. That is what we have distributors reps in the shop. I buy from them, they take care of me, I take care of my customers. I am a FIRM believer in the customer is always rite.
This is only what I would do. Has no bearing on what this dealer will or will not do for the OP.
CW