Yes, Monsoon stereos can be reset. I've never had to do it from mine, but I've heard that pressing a certain key sequence on screen will display a security code, and then you call some phone number, blah blah blah, and a computer tells you what keys to press to unlock it.
Or something like that. The phone number used to be public (I'm told), but it was changed, because they only want the dealerships to have access to it now.
Find another dealership. There's nothing wrong with it, if it's just locked.