Oh hi, first post but I'm here for sidesaddle info too.
There are only a handful of sidesaddlers left, worldwide. To compound the problem, there are only a handful of sidesaddle tree markers left.
The professional sidesaddlers are usually pretty cagey about where they source their trees, because it's a limited supply. But I know for english SS trees, Aulton & Butler seem to be one of the only commercial makers. For western trees, Wayne Swan makes them via Hundred Oaks saddlery.
There are a thousand pitfalls when making a sidesaddle, as demonstrated by all the cr*ptastic ones for sale on ebay. Are you looking to restore an old one, or to start from scratch?
To be honest, the best place for SS info is on a facebook group called Sidesaddle Riders! (yes with the exclamation mark) - active members include almost all the professional sidesaddlers worldwide, who are very generous with time and advice.
LindaF and Lillian (Linda Fleming and Lillian Chaudhry) are top sidesaddlers who are on the fb site. They are members of this board, but haven't been active for ages.
Other great sites are
http://www.sidesaddle.com/store/saddles/saddles.html - the site of the ISSO (International Sidesaddle Organisation), they keep the photos of all sidesaddles that they sell online as a resource
http://hundredoaksinc.com/overview - they make new western sidesaddles
http://www.sidesaddleassociation.co.uk/ - the british do everything properly!
http://www.lauradempseysaddler.co.uk/ - another professional sidesaddle maker who is very helpful
http://www.nickcreaton.co.uk/museum_gallery.html - Nick is an encyclopaedia of SS history
