The annual technical festival of Sant Longowal Institute of Engineering and Technology, Sangrur, Punjab (SLIET) is one of the oldest technical fests. Some of my close friends studied there, so I might be able to give you some basic information.
You can also visit the campus of SLIET (Techfest) and enquire about it on your own. Look for an application form that is specifically for the position of Campus Ambassador. Do not be surprised if there isn't any such program offered there. Just check their website or give them a call or just drop a mail to them asking about SLIET.