is dropped by one of the Guardians of BG's panoply (which is the "invisible Armor" you mentioned. I don't use it myself because it is impossible to tell if it is broken and the only way ro do that is to swap ir out with a piece of gear of the same type.It is that way because the previous owner (Sir BG) wanted it that way since he was not a showoff type,
I am not a modder, but rather a playtester (you can visit me on Emerald Isle if you want to get Expert Bow and the First Archer Promo).
If you need a playtester, I have plenty of experience (MM7 Mod. MM6 TCC, Wizardry 8 Lunastralis and Dodd the Slayer's V.1 thru 2.4 - Rise of the Ancients).
I would be happy to assist you as a playtester as I am very through.
P.S. I wouldn't spend too much time on the Blue Dragon Key as the rings in the chest don't work as advertixed. I missed that one in the playtest 