On my cinch thread someone pointed out that I have a 7/8 or 3/4 rigged saddle, and so even though I took along a wither form and it all “fits”, it might not be balanced for the pony’s conformation. There are quite a few vids on Youtube on how to put on a Western saddle, and at least one good one on how to fit a Western saddle, if you watch a bunch and weed out the junk you’ll get a sense of what you need for your guy.
Extra pads, um, forgive me but if they don’t work well to correct English saddles that don’t fit why should they correct a Western saddle that doesn’t fit?
I liked this vid http://www.youtube.com/watch?v=TtjATfeL6Hs even if it is sponsored by a pad manufacturer.
As far as finding the saddle, skip CL and go with something from a shop. The selection will be better and you might at least find out exactly what will fit him and be able to buy it new if you have to to fit both of you.