I have a shark fin withered horse and I was able to find a saddle that fit him and fit my needs as well. So don't be discouraged :)
The saddle, however, needs to fit ALL of him. His back shape, his topline, his width.. etc. etc. etc. so it's best to
a) rent a few saddles (saddles on loan before you buy them) and try them on your horse's clean, bare, back.
b) Check for how level the saddle is, how well it fits the curves of his back, and check for any pressure points.
c) Verify EVERYTHING with someone who knows what they are doing professionally (like a saddle fitter)
Putting pads underneath a saddle that doesn't fit.. doesn't make it fit. However, there are such pads (correctional halfpads) that you can use that affect the positioning of the saddle on the horse's back. But it is a bandaid and you should have a well fitting saddle regardless!
I think you can find one in western style, aussie style, or english style easily as there are many manufactures and many different designs.
I would just HIGHLY suggest that you bring a certified, respectable saddle fitter into the mix.