Q:
Arborist armor MIA
I believe that is cultural armor and can only be found in the Grove and can only be used by Sylvari toons. Since it is bound on acquire, you will not find it on the trading post.
Yes, the arborist armor is the T1 sylvari cultural gear for heavy armor wearers. It can only be purchased from the T1 vendor in the Grove, and may not be traded or sold. T2 is Warden armor, and T3 is Oaken armor; they have different appearances.
If you wanted to upgrade the stats of your armor without changing the look, you will have to get different armor and use transmutation charges to put the arborist skins over your new armor in the wardrobe.