There is also a store downtown by the bus station (is up the street from it, like 5 mins away walking distance) that sell a lot of bdu stuff, but ya, kw doesn't seem to have any airsoft part or gun selling based store. Your best bet is to go to toronto or order from the classifieds

^ABC surplus sells nothing airsoft just camo and equipment. Got my girl a pair of pants there, they actually had female issue pants!

you don't go in asking for an 'airsoft' battery then. tell them what you need in a battery:

brand
type (NiMH, NiCad etc)
total voltage (7.2, 8.4, 9.6 etc)
amperage
cell size
cell orientation
connector
length of wire

most hobby shops should be able to make it for you while you wait.
brand

for an AK stick battery to fit in the top tray you'll want:

brand - your call or what they have available
type - your call or what they have available
total voltage - 8.4v
amperage - 1400-1500mAh or what they have available
cell size - 2/3A (mini's)
cell orientation - in a stick obviously (ie all lined up in a row hahaha)
connector - your call. don't know what's on your AEG
length of wire - not very long