This is my "go to" place for costumes in Toronto. Now mind you, I don't find many of my high end pieces there unless I go next door to their rental department, but they do have all the basics.
We have gotten 2 of our Santa costumes there and they were at a great price and more convenient than having to do mail order. For certain special pieces I have gotten then to do a "special order" and bring them in, although at that point I often do mail order from places online.
Get your creative juices flowing by stopping by and I'm sure you will find something you like or at least get a good start into getting a perfect costume!