If you exit the Mitake station a little bit down the road on the lefthand side there's an outdoor store Maunga where you can rent a pad for the day (1000 yen if I remember correctly). I guess they will sell the topo there also. Tokio Muroi's black book Mitake-Mitsumine-Ogawayama topo is good and cheap. Otherwise any other climbinggym with store in Tokyo will sell it too.
If you climb on the weekends Mitake will be so busy with climbers you will probably not really need an extra crashpad or topo, there will be plenty around anyway. Though it's nice to bring your own crashpad ofcourse. And remember Japanese climbers don't like you to step on a crashpad with walking shoes for reasons of politeness.
Mitake is a pretty small area but beatifully situated at the riverside and fun too in my opinion, enjoy!
google translate might be able to help with some of the Kanji.
hope you get good weather ... it's been raining in Tokyo lately (actually, yesterday night until this morning). if it rains hard enough some areas in Mitake will be flooded by water run off from the nearby mountains.