Is there a good place to get these?

According to another quest that's been in my log for the last year or so, the cores are supposed to come from "a dungeon deep in the Ilmari desert" which is not precisely a location description that fills me with joy... Are there alternate places to obtain these? How far into the dungeon do they drop and from which mobs? My friend and I are able to duo manticores but rather shakily, so I suspect we will not do too well in the dungeon on our own.