try Tudor Equestrian in Edmonton. They might have used saddles in that size.
E-Bay has a lot of sellers who ship to Canada, and I know there is a good group on facebook called English Tack Exchange, and I believe the English Tack Trader. You can always put an ISO of add in those groups.
Have you searched for any Crosbys? They used to go up to that size...Thornhill I believe I have actually seen in a 22" before!
Definitely doesn't need to be new, just can't seem to find anything that big.
I live in the US, but I am sure you have access to many of the same brands. Something brand new is hard to find for that price especially in Canadian currency...but i'd check around at any tack shops they may have used or consignment saddles. Dover saddlery also has adjustable saddles in their brand Circuit now, but many are more around $1200+. Ovation, HDR, Thornhill etc may make something may offer something more in your price if you really want something new, otherwise I would look online and keep an eye out theres a lot of great facebook groups with quality used tack.