Hello,
First off...I hope your brother is feeling better after his run it with that dog.
When selecting a brand of pepper spray, I usually prefer a blend of CS & OC (CS is tear gas & OC is pepper spray), and one with a dye that will "mark" an assailant for a period of time, which aids in identifying the aggressor if needed.
Here's a couple of law enforcement website, where you can purchase whet you want. All are law enforcement grade, and should do the trick.
http://www.galls.com/
http://www.streichers.com/