For Nagpur, I confirm it is not possible to get a crew visa on arrival. Plus I highly recommend to avoid this stop.
We did a fuel stop there a few months ago (refueling was ok, avgas available), and due to weather conditions we requested to stay a few hours in the transit area, as we knew we couldn't enter the country. The local agent rejected our request, and did everything he could to make us leave asap, including threats to have us arrested if we did not depart quickly
Awful service. I won't stop there again unless both engines are out...