The Modern Bajaj Chetak Rides On
The Bajaj mirrors are unique and many riders have struggled with finding replacements.  Here are some alternatives:

(A) 8 mm adapter bolts to adapt to the thread of the new mirrors.
(B) Clamp-on Vespa legshield mirrors clamped to the legshield or to the Bajaj front rack. 
(C)A universal mounting solution:
The original mirrors are very stable, due to the extra thick shaft, but mostly due to the double bend. That takes a lot of the
vibration out. To change to other mirrors, get an allen head
screw of the same thread count, but about an inch or so longer. Put the new bolt in from the top, where
your mirror used to be. Add 2 collars(they are kind of like washers but are about a quarter inch thick...they
usually have a tiny allen set screw in the side). These washers should extend slightly below the bottom
of the headset hole. You then can add any  Vespa or Stella  mirror bracket. The brackets (pictured) look a bit like a boomerang with 3 holes. You can mount any mirror then, either in the middle hole or the outside hole. You also have
more options related to Windshield choice. As far as vibration, any choice will most likely vibrate a bit
more than stock at idle. A straight shaft can transfer vibration much easier that a bent shaft. 

The Modern Bajaj Chetak Rides On The Modern Bajaj Chetak Rides On