How do i do a Garrison Lv40??? Pls [Help me out!]Follow

Yea, i am lvlng my war/nin now and it's lv40/20 and i want to get into a Garrison 40 because i saw this newitem called an Agile Mantle and it adds +1 Accu and +1 Agi and it will help me out a lot better than my current Nomad's Mantle, but yea if anybody could possibly tell me what to do for a garrison, or where to get quest i'd really appreciate it, ty.

-Falo