Martin,
There are many shifty operators selling bikes all over India. And in Delhi.
I spent a year and a half riding about india on a 350 and over that time had plenty of work done on the bike.
Plenty of parts everywhere for 350s. What I learned was that any old bike that has a straight frame and sound engine block(no cracks or stripped bolt holes) with paper work and matching numbers is a good place to start. Buy one of these cheap from a farmer in the middle of nowhere even if it is not running. Get it to your trusty mechanic and rebuild the bike. New everything. Wheels, tyres, electrics front forks that have disc brakes, rear brakes, seat, a Pujabi muffler, cylinder, piston(Original not copy), rockers(old steel type), have crank bearing done, airshocks on the rear and new torsion bars, new clutch bits, rebuild gearbox, other new electrical bits and a new paint job should see you just about done. But one more thing, a loud horn, the sort that gets fitted to the front of trains to alert those around you that your are just about to do something stupid. Always sit with the mechanic even if it takes days to do the job. The next mechanic you visit will want to steal all the good bits and put in old crap whilst you are sneezing or ducking out for a chai and a smoke.
My mechanic friend helps to run the bike in running the bike over night on a couple of tanks of fuel at varying revs. Saves riding forever at 40 ks an hour. After the run in and a change of oil I found a can of Nulon and stuck that in for good measure.
Beware of inviting gaps in roundabouts, racks of two foot high speed bumps hidden in shadows.
Be sure to push your way to the front of any congestion such as those at railway crossings.
Go to Jaipur. Call my Mechanic Friend Almas +919828233938 and say Australian David recommended you if you find Delhi a bit much. It is only a few hours away and pleasant enough place to stay and a good starting point. Head west to Pushkar (Lotus Hotel on the other side of the lake) Jodhpur then north.