There is rather little here, but these are your best options for fixed friendly:

Joe Mamma's: 216 Pretoria Ave. < http://www.joemamma.ca/index.php?section=about >
(Just south of the Quenn'sway, off of Bank St.)
They stock KHS Flite, but are mostly a BMX/urban/cruiser/snowboard shop. They are always happy to order parts. I always stop in and fill my tires there, because I can't get high enough PSI in my hand pump.

Cyclo-Sportif G.M.bertrand: 167 rue Wellington < http://www.gmbertrand.com/ >
(Across the river in Hull)
They are planning on increasing inventory for fixed and SS parts. This shop is aimed at high-tech roadies, but is never snooty. Last time I went, they only had cogs, but i know alot of people have gotten parts through them. If you need a good mechanic, go there. I should be getting Miche parts and some Chrome bags, I believe.

Bike Dump: 407 Catherine < http://www.bikedump.com/ >
(One block north of the Queen's way, between Bronson and Bank)
Anything used, it's there. They have oodles of parts, all organized in bins. I bought a pair of flat handlebars, grips and a white Selle/Bianchi saddle there, the total was $10.

All of these shops give discounts to couriers as well. I have been to every shop in the city, and found these to be my faves.