Not got a part number, but can reccomend the Twinair from TotallyTTRs http://www.totallyttrs.com/#Twin_Air_Filter (only compared with standard - never tried a K&N on it)
Current: Suzuki RG 125 Gamma, Armstrong MT500, MZ ETZ300, Triumph Tiger 885i, Kawasaki GTR1000, Kawasaki GPZ750, CZ175 Trial, Yamaha TTR250 RaidTomorrow's just another day.
Prison, if you build it, they will come.