Feywild saga has shadow weapon mirrors idk if those will work for you
That's not a generic Mirror of Glammering, which makes a cosmetic duplicate of whichever armor/helm/goggles/cloak/weapon you want to make cosmetic. The Feywild saga has the "Illusory Shadow Glamered Weapon Aura" which is exactly what it says a cosmetic weapon aura that AFAIK can only be applied to an already glammered (cosmetic duplicated) weapon. E.G. you
need a Mirror of Glammering and
must use it on an applicable weapon in order to
be able to use the Illusory Shadow Glamered Weapon Aura from the Feywild Saga.
AFAIK you can get Mirrors of Galmmering
from the store, from DD, from (FREE) store coupon promotions occasionally, from expansion pack bundles sometimes, I seem to recall there is or was one other limited time bundle that I thought had Mirrors in it but I cannot remember exactly what it was called and searching the wiki isn't helping. It was something like Weapon Rack.
Do they ever drop randomly in-game? Idk. I thought store items were supposed to but the drop rate is so inestimably low I haven't had anything outside a skill tome or minor xp pot in years.