This is my second attempt to post...you could contact George Wittemyer at Colorado State University. He is experienced in working with collated African elephants. 

Hi Cheng,

I know the folks from Danau Girang in Sabah, Malaysia have done this a few times with Bornean Elephants, check out the website

http://www.cardiff.ac.uk/danau-girang-field-centre

and get in touch with their Director, Dr. Benoit Goossens, I'm sure he'll be able to help you with some advice or literature.

Cheers,

Paul

Hi Cheng,

Under no circumstances should you undertake a project involving animal anesthesia without having a qualified and experienced veterinarian on your team.  Contact your nearest zoo that has Asian elephants and find out who their resident veterinarian is.  Make sure that they have anesthetized an elephant before....if they haven't, find out who the nearest one is and make sure to get them on board with your project (even if it means only in the beginning and just to train a more local vet in procedures).  In any case, only resort to anesthesia and collaring if you have no alternative to gather the data you need.  Good luck.  J

You have to involve the veterinarian so that he/she better knows the anesthesia, and dose. But to shot elephant, first you have to separate a targeted individual from group and follow the elephant until that reaches to good terrain. Once you shot elephant, drug will start working after few minutes and that time, elephant can escape from the vision, if terrain that you select to shot is dense forest/hilly. So, you have to consider these before hand.

Good Luck!