What saddles fit a more high/narrow withered horse? 

Something older. All these new saddles seem to be for round fatties. 

My mare sure isn't a round fatty. She is built and her withers are not as tall as other horses. It's tough to fit her with a saddle that doesn't roll.

Larry Coats

Have lots of experience with this...narrow and tall wither, especially. Getting close to 65 different kinds of saddles I've tried on this type of horse and a common theme.

Best two I've found are Len Brown and Vernon Purdy saddles.