Well, you could perhaps try the
Sivananda Yoga Vedanta Dhanwantari Ashram at Neyyar Dam in Kerala or the Sivananda Ashram in Rishikesh. I personally have not visited either of them, but I just met a yoga teacher here who trained at both places and was very impressed. Other than that, if you really want an ascetic experience you might seek out the Bihar School in ...somewhere in Bihar (I don't ...