I don't know what the E-6 situation is in India but you could get an E-6 kit (they cost $20 in the US) and develop yourself. The Tetenal kit comes with instructions on pushing (1 or 2 stops, I believe) so you could extrapolate a bit for 3 stops. That's about the only guaranteed way to do this. Trusting it to a lab is fine, if you have a good reliable lab. If not, it could get processed "regular" by mistake and you'd have very dark images.