As conveyed by Nitin Amin:
The thumb hole for pancham is indeed getting quite popular, and many flautists want to use it. Most bansuri makers also have started making bansuris with this hole... A word of caution though: the ease of using this hole depends upon the way you hold your flute. It becomes extremely easy and quickly adaptable if you use finger tips for closing all the holes....For the more conventional method of using the middles of fingers, you may find it quite hard to use this...
You can get these flutes at Dhotre Flutes (https://www.dhotreflutes.com/), Punam flutes (https://www.punamflutes.com/) ref: Subhash Thakur, Nadvenu (https://nadvenuflute.com/) ref: Raju Salve, Radhe flutes (https://www.radheflutes.com) ref: Tejprakash)