The easiest way to find out who registered the SIM card to access the databases of mobile operators. The data specified there, as a rule, untrue, and are taken from the contracts for the provision of mobile communication services concluded with subscribers. The main thing is to look to the database as "fresh" because it is derived from information loses relevance. To buy such a basis can be at Gorbushka, Mitino or on Savelovsky radio. The cost is certainly not small, but the horizons opening up to you, too.
Try to find friends who work in the company the mobile operator. Certain staff members have access to information on registered subscribers. Despite the fact that the security service is up and harshly suppresses any kind of information leakage, you may be able to negotiate to obtain such services. The question of motivation your friend will depend on the relations in which you are.
Try to find out who registered the SIM card through the payment service provider. After all, when the funds are credited to your account Manager verifies your number with the information taken from the database of the operator, available on the computer. If you manage to bluff so that you don't got to invent a legend to soften Manager, you will get the information you need.
Contact private detective Agency, which in recent years is quite large. The Agency's employees, usually former policemen or KGB boys with good connections and powerful administrative resource. Your problem they will solve in a matter of hours, making a few phone calls of "where necessary". But services of this kind will result in you "a pretty penny". But you can be sure the purchased information.