If you are selling just to get rid of it, any dealership will take it. Of course, you won't get much for it either. That's the trade-off, get rid of it immediately at a low-ball offer. Or sell through some other venue with a higher price and it may never sell or you may be waiting for a long time.
By the time the unit actually sells, and your 3rd party intermediary gets their commission cut, you might have been better off just selling to your dealership and been done with it.
If you are upside-down on a loan, you'll never get the price you need to pay the loan off, from anywhere.