I've seen a area with them before as a random encounter... but the name just won't come to me. I can describe it very well, I just don't remember the name!

When you first fight with Mustadio as a guest, when the people are chasing him though the city. He begs you to take him to see the Cardinal. The next main event is when the same people are after him again.

This time, you're fighting on a mountain-like area. This is your first fight that includes the ever so annoying summoners.

It's this area that I see random encounter summoners more often.

Hope this helps Nakor!