Japan festival is usually some time in September,
But
There is also the Japanese Sakura festival normally some time in march or April but it seem to have been toned down the last couple of years I think due to weather.
I have kept an eye open but haven't seen anything listed as of yet
And lately some time in the summer around the 7th of july they have the Tanabata festival
If I hear of anything I will post, there is something this weekend but I dont think its a festival
Also they have a web site
http://uwajimaya.com/store_events.html