The guys at G3 in Chiangmai can get you the right size Dunlops from Bangkok so thier about, but avoid the local Dunlops and go the Jap ones, the local ones are OK for about a month, then thier useless, just ask big & tall who was sitting in the box seat behind me on the Samoeng loop when mine let go. Another good mod for the CBR 150 is to get one of those gas shocks that fit those little Kawasaki KSRs, thier about 2,800 Baht you have to knock a little bit of metal out of the bottom mount on the swing arm to allow it to pivot forward a bit and cut a nitch out of the plastic on the left side below the seat to fit the gas bottle but it makes a huge difference to the handling, also dump the oil in the front and replace it with a heavier one and pre load the springs about an inch. I went up to Pai on mine and that last 30 klms where it gets real bumpy didnt bother it at all, it just soaked it up, admittadly the recoil damping on the shock is a little slow and has no adjustment but even on the Pai road it didnt seem like it was packing down, the other thing to do is raise the pegs, too low for serious cornering
John