Welcome to Tokyo. Actually quite a few of us that stalk this part of the forums are prior and current military. Prior AF myself.
Anyway there are a lot of events around the area, just they are a little different than events in the US. Japan doesn't have "Cons" in the Western sense although there are a few large events that generate a similar feeling. In Japan, Cosplay is kind of its own separate entity so cosplay is usually done at cosplay specific events although some large hobby related conventions allow cosplay. So events can vary in size from small photo studio gatherings to large-scale events with over a thousand cosplayers.
Some large foreigner friendly events in the area are:
Comic Market "Comiket
": The largest amateur comic market in the world. Averages 500,000 attendees. Last event saw 8,000+ cosplayers. Held twice a year at Tokyo Big Site in Odaiba. This year's dates August 10-12 and December 29-31.
Wonder Festival: The largest amateur figurine/garage-kit convention in the world. Held twice a year at Makuhari Messe in Chiba. This year's dates February and July 29th. Cosplay has become quite popular there.
Tokyo Game Show: Japanese video game industry trade fair. Held once a year at Makuhari Messe in Chiba. This years dates September 22-23.
Tokyo Fashion Town "TFT
": A large cosplay only event held multiple times a year at Tokyo Fashion Town's event hall in Odaiba. Not sure on all the dates, but they always hold events at the same time as Comiket. Some Japanese ability recommended.
Not in the area, but worth going to once for the experience is the World Cosplay Summit in Nagoya. It's in early August.
Aside from these, most cosplay events are small scale cosplay only events. These small events are held almost every weekend somewhere around Tokyo. Cure Cosplay
has a good event calendar, but it's only available in the Japanese section of the site.
Just so you know, randomly walking around in cosplay in public is very frowned upon, this includes Akihabara. Because of this cosplay events prohibit cosplayers from wearing their costumes to and from events. You must change at the event, which will provide on-site dressing rooms. Exception being Gothic-lolita because it's considered street fashion and not cosplay.
Enjoy Yokota, y'all have the best BX in Japan...