Look harder for suppliers... You cant beat the stock size, the 120 will fit but you wont like the feel and there will be less of a contact patch... Try and sort your tyres out before you hit the track, Youll have a better selection...

Alpha 10's are good road/track tyre they replaced the GRP70sp or Bt090's or if you can get them i run with 209gps there awsome but very expensive!!

Best of luck!