Diploma in Urdu is offered by very less colleges. Now as per the records there are four colleges all over India which offers a Diploma in Urdu course. These colleges are:

General Shivdev Singh Diwan Gurbachan Singh Khalsa College, Patiala

C Abdul Hakeem College, Melvisharam

Rouzathul Uloom Arabic College, Kozhikode

Tauheed Institute of Information Technology, Katihar

But in any of the colleges official website the eligibility and the process of admission isn't mentioned.

I hope this answer helps. All the very best for your future endeavors!