Saddles direct bought one from me, obviously for less than they would sell it on for, but it was a quick and painless transaction!
Ebay also good but put a low start price and hold your nerve!
Saddles not making great money at the moment so you have to be realistic
You'll get more for it selling it private or on ebay or fleabay as I like to call it
If you want a fast sale, a saddler will take it in part ex but they will give you peanuts for it and you'll then see it on their website for double what they paid you for it, so I'd sell it yourself first, you'll have more to put towards your next saddle then.
Livery yards/competition yards/tack shops/Freeadds/Preloved/Ebay, just spread the word and you'll sell it no bother, I'd just sold a Farrington Burford Event, sold it cheap for quick sale but a saddler would of sold it for double on their website, second hand saddle market is catch 27 of the horseworld.