How to get the salary details of wife from a private unaided school for maintenance case

Hi Experts, I would like to know what the different ways are to get the Salary details of Wife from a Private unaided School and Bank statements showing Salary details for Maintenance case. I tried to check different blogs and found that RTI is not applicable for unaided private international schools, Hence need help to understand the steps. Secondly what are the steps to get the bank statement of a wife crediting Salary from the school from a Private bank, Pls suggest the steps and options for the above. Please revert. Regards, SR