Not sure about this, but you can try SBI (Mauritius) Ltd ATM, most likely it'll be free. SBI doesn't charge anything extra here in India for foreign cards. SBI (Singapore) Ltd also has no extra fees in Singapore. So, there is a chance that SBI Mauritius won't have fees as well.
Update your findings here, it'll help other fellow travellers in the future. Have a great trip.
Thank you, still confused about using Kotak 811 metal DC. Website doesn't mention any wrt to withdrawal charges but on customer care call they mentioned free but I'm not sure about them.