Have you tried ebay? I have size 10 feet and always find a bargain there, also Saxone have a good big feet department, long tall sally and failing that a trip to the u.s.a to the payless store!!!!
Payless Shoe Source is a good bet for big feet (they go up to size 13 for women!) And they are all over the U.S. and Canada. They also have a website to order shoes from as well.
tall girls, medissa, magnus, emotion, long tall sally, cinderella evans (sometimes the wide fitting 10 is good if your an 11), all of these have good websites and go up to 11/12 converses! they are fab and the larger men's versions are just as good as the womens