Respected Sir,

IISc is he best college in India currently and there is no direct entry. You need to earn your way into it either by KVPY , NEET or JEE advance. 

And for Tamil Nadu Colleges ,you need to apply for TNEA , a counselling based purely on Board marks. 

And for private colleges like SRM, kindly contact the college people itself. They would help you for direct entry.

Hope I was able to help you.