Craigslist.
Even if it is not working you can offer it on CL, someone may be looking for other parts on your fridge that are good.
Things like control boards, door hinges, door seals, compartment parts which often break and either are expensive or not available at all may have some value to someone.
I have seen "working" RV fridges offered on CL for as much as $500, someone is bound to be dumb enough to pay for a used "working" RV fridge.. Lots of die hard RV fridge fans on this forum would be glad to find a used working pull (just don't "advertise" it on this forum which would be against the rules)..
Barring CL and if all else fails, call your local garbage hauler and ask if they take RV fridges, some may for an additional small fee.