I am preparing for neet from past 2 years by self studying.At the time of admission in medical college,from where I can get gap certificate?

You neednt produce a gap certificate. It was your choice that you have decided to take a break and focus on your goal. MCC guidelines do not speak anything about requirements for a Gap certificate. All those documents you might need are your 10th and 12th certifucates, 13th standard certificate, NEET admit card, NEET rank letter, Category certificate if applicable, PWD certificate if applicable, proof of Date of birth, proof of identity, 8 passport size photographs and provisional allotment letter.