We know the Allagans could manufacture aetherites instead of having to use "natural" ones like it currently done. So I wouldn't be all that surprised to see Allagan-style aetherites in Garlemald.

One thing to keep in mind is that 1/3 of the "native" Garlean population isn't even racially Garlean. So I could see the Garleans always having aetherites for the use of the non-Garleans that have always lived in Garlemald.