+7 bloody boned garrison (if you wanna kill yuorself upgrading a garrison to 10)
how to get it?... its a quest... in the gunslingers guild( where you become a gunner) with an npc called "garrison"
i dont remember the items, he will give you a garrison[1] then you have to do a quest with mr garrison again (yeah pretty boring) to get the second slot
its all XP