There's three dive-shops that I know of in KW, and they've all been named... Groundhog divers, Tri-City diving, and Deans Sport and Dive.
They're all on Victoria, east of downtown kitchener.
Groundhog is easy to spot; tri-city is tucked into a little mall on the south (right-hand as you head out Victoria) side of the road, but if you
watch the billboards it's not too hard to find. Dean's, on the other hand (at least as of a few months ago) doesn't have a sign up on the road.
They're no longer out on that dirt road in Breslau, but are now tucked in the back/bottom of a small mall; just about the last thing you pass on the right-hand side of the road before you head out of the city towards Guelph.
Dean's is, however, about the "techiest" of the three shops, at least from what I've seen. I know they do Nitrox, and might do trimix as well.
The staff at all three shops are very friendly, and have a very good attitude about people coming in to browse and ask questions, even if you're not buying.
Jamie