There are many ways through which you may approach corporates to place your students for internship.
option 1 : Visit job fairs and meet company recruiters directly. You will get an opportunity to interact and introduce yourself to them. in last, don't forget to exchange business cards for future correspondence.
option 2: you may Contact shine.com. They have a separate division for campus connect. They play a role of mediator to connect institutes with corporate. it will be direct source for them. Similarly identify more such companies in the market.
option 3 : Improve your network through attending HR conferences, seminars etc and build relationship with corporates.
option 4: Invite HR spocs in your institute as guest lecture
Trust the above options will help you to initiate the process and connect corporates