it looks like the xt8 has the same spur gear as the Losi 8 and the Associated RC8. i think you could buy one of those and it would work. if you cant find anywhere in japan that sells them just find somewhere in USA that will ship internationally.
i could not find anywhere that sells the spur for the xt8 but here are some links for the spur for the Losi and Associated which should fit your Xray.
http://www.impaktrc.com/advanced_sea...ords=spur+gear
http://www.losipartshouse.com/servle...s?sfs=d6f064e2
http://www.losipartshouse.com/servle...s?sfs=d6f064e2
http://www.losipartshouse.com/servle...s?sfs=d6f064e2
http://www.amainhobbies.com/advanced...words=spur+rc8
http://www.amainhobbies.com/advanced...robinson+8ight