Source: As worded by Indian Railways, Government of India

Yes, you can approach authorized Rail Travelers' Service Agents and Railway Tourist Agents, who will book your tickets on payment of prescribed charges. No separate reservation quotas have been assigned to these agents and their staff have to take their turn in the queue at the Reservation Office for purchasing tickets like any other passenger.

Addresses and phone numbers of these Travel Agents can be obtained from the Station Managers. Please do not buy tickets from unauthorized Travel Agents.