Those 3 locations mentioned are the only 1's with any real spawn. South of Mega Volt, mixed with other mob, sparse spawn at best, north of Solfais, largest spawn I know of, mostly young there, and the PVP area by Aegis Mound, though the spawn is medium in there the gen is mixed from a few Young to Alpha
Haven't seen or heard of any new spawns to support mission yet, if anyone finds new spawns, please post location in this thread. gl hunting