Hi Guys, need a little help here

I'm looking for the three dawnguard agents who supply hidden caches out in the wilds of Skyrim. I want to know, where can these 3 guys be found? is it simply random chance, ie I run into them walking the road? or are there specific places they are at? Any help will be appreciated.

This should be in the dawnguard forum

Ninja'd

Sorry guys, Mods if you could kindly move this to the spoilers section, i'd be much obliged.