Re: Dojos near Hiroshima / Iwakuni area?
A quick search for "Iwakuni aikido " seems to show an aikido dojo off post. I'm sure there is information available on-base. There are different styles so you might want to inquire beforehand or at least have a look-see. It wouldn't hurt to ask about the teacher's rank and background. There is an English phone book so you might try looking up aikido once you get to Japan.
I live in Kitakyushu, which is just over the Kanmon bridge in Kyushu. I've been through Iwakuni and it is a small town so commuting to another town for a more suitable dojo would at least allow a change of scenery.
Also, I would ask a Japanese person. Someone studying karate/kendo/judo (which is more popular than aikido here) might have knowledge of dojo other than the aikido class advertised
Good luck and welcome to Japan!