The way to virtually guarantee a sale is to put it on ebay with good photos from every side and accurate measurements. Of course you take your chances on how much money you might get. Otherwise ask a saddler to sell it for you, but it might sit there for a year.
I am currently selling a saddle on ebay it seems to be selling well and has a few watchers. When you take the photos make sure you "dress" the saddle up with a fancy saddle cloth and stirrups but make sure you state they aren't included in the sale. Also try and make the auction end around 7-8pm on Sunday night as this is supposed to be the most popular time for people looking on ebay.
It is a bit of a lottery but you could set a reserve as a safe guard.
As for sending it to the winning bidder, a large box is required (pad out the gaps between the saddle and the box edges with some plastic bags) and a trip to the post office! Will cost approx £20 I think.
I think that there is qite a lot of people who will buy saddles on ebay. I have been having a tack room clear out, and have sold 7 (yes really 7!!!) pony saddles that were sat doing nothing. They all went for a good price.