How to find track/Keirin races when travelling?
List of upcoming keirin races: 
http://keirin.jp/pc/raceschedule 

List of velodromes in Japan: 
https://en.wikipedia.org/wiki/Category:Velodromes_in_Japan and http://keirin.jp/pc/jyolist

If you need help translating the page, Google Chrome's auto-translation is pretty good.