Real Canadian Warehouse Club. There are two locations in Calgary. They cater primarily to restaurants and businesses. They carry a lot of restaurant supplies. Good prices too. Note though that they only take cash and debit.
If you want a fun experience try BJ Restaurant Supply on Centre St. N. This place is chock-a-block with restaurant supply equipment. Fantastic prices. Their business targets the asian restaurants in the city. Fun place to poke around. You will find some interesting stuff for sure.
I have two beautiful racks I bought at Williams Sonoma. Fit a large sheet pan perfecty. I would also try (may be cheaper):
Russell Food Equipment Ltd -
5707 4 Street SE, Calgary, AB T2H 1K8
Brown's Food Service Equipment Sales Ltd
403 Riverfront Avenue Se, Calgary, AB T2G 0C2
(403) 262-6009 Cash only
How about a restaurant supply places such as Hendrix:
457 - 42 Avenue SE
Calgary, AB T2G 1Y3
I believe what you are looking for is a cooling rack that fits a full sheet pan... it would mainly be restaurant supply places that carry it as the full sheet pans don't fit in most residential ovens.