According to my knowledge National institute of technology colleges offer admission in M tech courses only through GATE entrance examination. To get admission in NIT colleges you must pass GATE examination. Many other colleges offer admission in M tech through other engineering exams .

M tech engineering exams:

Bharath University Engineering Entrance Exam
BITSAT Entrance exam (BITSAT)
Dhirubhai Ambani Institute of Information and Communication Technology Entrance exam
GAT Gitam University Online Entrance Test
BSAUEEE-B.S. Abdur Rahman University Engineering Entrance Examination
Calicut University M.Tech entrance exam
International Institute of Information Technology (IIIT) Bhubaneswar M.Tech Entrance exam
Kalinga Institute of Industrial Technology Entrance Exam
KARNATAKA CET
Post-Graduate Engineering Common Entrance Test (PGECET)
PTU CET
Regional Institute of Science & Technology (RIST) Meghalaya - M.Tech Entrance exam
SRMEEE SRM Engineering Entrance Examination