Annamalai University, Chidambaram, and Madurai Kamaraj University (TN) are a few universities that offer one-year Post Graduate Diploma courses in Labour Laws & IR. As you are from Delhi, you may consider approaching some reputable management institutions such as:
1) Faculty of Management Studies, Delhi
2) International Management Studies, New Delhi
3) Asia-Pacific Institute of Management, New Delhi
and explore their offerings.
Thanks