A good store to purchase brake pads from is Parts Source. You can even ask the employees for tips and pointers if you are not completely confident in replacing brake pads.
According to customer reviews the best brake pads and rotors are EBC brake rotors and pads. They are manufactured in Britain and can be found at any auto store including Canadian Tire in Canada.
Purchase a repair manual for that vehicle from your local auto parts store if you are not familiar with brake repair.
One can purchase Hawk brake pads online at the official Hawk Performance website. Another website that offers the brake pads is the official Tire Rack website.
While it may be possible to purchase used brake pads, you should not buy used but usuable brake pads. You should only buy new brake pads in excellent condition.
You can get brake pads from any outdoors store. There is not necessarily a particular sale on, since you will need to make sure you get brake pads that fit your brother's car.
You can purchase very inexpensive brake pads for as little as $15. Brake pads can also run over $100. The price will depend on the quality of the pad and the make and model of your car.
Auto supply store (I have have good luck with mid range)
GM brake pads are a good way to go but they are really no different than any other brand of brake pad. They all do the same thing. I am sure you could get the safety rating from an auto parts store.
Purchase a repair manual at any auto parts store.
Purchase a Haynes Manual at your local parts store and it will take you step by step for if you do not have illustrations, it may be confussing.
One can purchase EBC brake pads and rotors online from stores like Auto Anything, EBC Brakes Shop, RDA Brakes, EBC Brakes Direct and eBay. These brake pads can also be purchased from other sources than the ones specified.
Go to your local Canadian Tire store and purchase a Haynes Manual from auto parts. This manual will help you greatly for many different things, and only $20.00. Good luck.