There was another rare encounter at Germinas Peak (?):

You have to enter the place from Zarghidas Trade City. Reaching it from Poeskas Lake won't work, as you occupy their positions on the battle.

The rare encounter consist of a group of chemists and Mediators, but the important thing is that they carry rare guns! Not all of them, but at least you can expect them to have 2 guns.

You can get the Stone Gun, Blast Gun, Glacier Gun, and Blaze Gun that way, if you couldn't get them.

Another "rare" encounter, is at deep dungeon, at VOYAGE.

You can face a lot of archers there, and the good thing is that sometimes an archer of them may carry a Yoichi Bow. (I've got an extra one this way.)

And at last, there was this interesting encounter at yuguo woods, a group of samurais that have one of each katana equipped. Except the rare ones, thought.