From Ariadne in Caid:

Some resources for jousting saddles and medieval saddles in general:

I've dealt with this outfit before and they are great to work with. Have made several saddles for pro jousters and SCA equestrians. Costs are right in line with the cost of a good quality modern saddle and everything made on custom built trees (McClellan type). American Military Saddle Co.

Good info on types of modern saddles that can pass as period:
Narrawin Stud

Some good discussion/Info on modern saddle trees and how to fit them:
Leatherworker.net

FireStryker Living History Forum (scroll down for some great pics of people's creations)

www.sellerie-phoenix.com/slicea.htm (craftsman in France who has made saddles for several of the Pro jousters I know. Speaks English and is easy to deal with via email).

Double Branch Saddlery (these guys make saddles for the SASS types, but have made SCA and Medieval saddles too. Good quality saddles)

Some good info on period saddles in general: Classical Fencing

Duke Armand's saddle making instructions:Site 1 and Site 2

Some nice pics of a jouster's self-made saddle based on the extant example of the Henry V (scroll down the page to see the pics): Wasson Artistry

British saddler making "medieval" saddles on modern trees: Hightower Crafts

Some really cool "baroque" tack (bridles etc) from Russia and eastern Europe.
Traditional World Heritage and Fine Tack