Dareck, this is what I used. It's for Garmin MapSource, but the other poster mentioned a tool to convert to your GPS unit. I was in Osaka, Nara, Kobe, and Kyoto and was successful in locating caches with these maps.
http://www011.upp.so-net.ne.jp/mametaro/index-e.html
http://rwsmaps.griffel.se/