If you ever lose your SIM, it is often easier to go for a new SIM as it costs less than a Rs. 50. Moreover filing FIR with police isn't a easy affair, given the cost of bribe.

If you want fresh, never allocated SIM then better go for any number whose series is very new. For example avoid numbers which start with 9. Better go with unheard of numbers which start from 8 or 7 etc. Try to find series of Aircel, Uninor or other smaller players and see if those are some new looking numbers.

Or better note down the phone numbers from the SIM card at the shop and try registering at IRCTC, whichever works, just buy it.