Where can I find rear brake pads (??) for a 2008 Yaris?

[MisterFreelance]

Rear wheels started squeaking a few weeks ago when the brakes were applied, and our local mechanic recommended we get replacement pads (if it is indeed pads that we need) for them to install -- cheaper to bring the part than to buy it through them.

The thing is, I can't figure out where to GET it. At Canadian Tire, they say that they "aren't available" (at both C. Tire outlets here in Sherbrooke, Quebec). Beyond that, there aren't a lot of chain car parts stores, and I don't really know WHAT I'm looking for in terms of the exact part I need and if there's another "version" of it that would work.

Can somebody point me in the right direction?