If you're looking for Halloween decorations and costumes here are some places you can try:
The Party Bazaar: (Vancouver and North Vancouver) Overpriced, but they have Vancouver's widest selection of Halloween items.
Thomas FX: (North Vancouver) Some things are overpriced, other prices are fair. They have a lot of unique items. Many items year-round.
New York Novelties: (Main and Broadway): Some goofy stuff, some scary stuff.
Dressew: (Downtown Vancouver) Masks, Wigs, costume accessories. Few decorations. Good prices on fabric to make your own costumes.
Homesense: Lots of reasonably priced decor and kitchen items. Some props and costumes.
Spencer Gifts: Not a great selection this year, but they have both costumes and decorations.
Walmart/Superstore: Check them out, some good prices, and sometimes some cool items.
Value Village: Mainly costumes and accessories, but they have some decorations.
More Madness Costumes: (Fraser St.): They rent and sell costumes and accessories.
Shoppers Drug Mart: Every once and a while shoppers has something really cool and often affordable.
HollyNorth: (Burnaby) Mainly theatrical makeup (bloods), but a couple severed limbs. They also rent gear and have great supplies like nicotine spray and snot tape.
Micahel's Crafts: They put their stuff out early, and transform to x-mas before Halloween which is good in the sense that now what's left is all on sale. Some neat props and decorations.
Carols Costume Corner: (North Vancouver) Mainly sales and renatls of costumes and accessories.
Spirit Store: (Burnaby) A large store with some cool props and lots of costumes. Not as many products as I was hoping for.
I am in no way associated with any of these merchants and am not linking to them on purpose, however a quick web search should bring you their info.