The Himalayas? I've been mulling over the feasibility of pulling a Grand Fenwick out of one or more of the old Hill Stations (to those not familiar with British India, a Hill Station was a mountain resort where the governing class of the British Raj could retire to in order to get away from the summer heat) by having the government of the Raj set aside a handful of mountain valleys as pretty much exclusively for British use - encouraging small scale British settlement (demobbed soldiers would be ideal), discouraging Indian settlement, investment and infrastructure to European standards. Start in the mid 19thC in somewhere like Arunachal Pradesh (still the least densely populated part of India today, IIRC) so that by 1948 it has a population of 50-100,000 white British (if you don't look too closely, many of them will probably actually be mixed race after a century or so) English speaking and nominally Christian inhabitants which is separated off by the British as independence approaches to become its own state whose existence is tolerated by India as it acts as a buffer with China.