Yes, you can file RTI to obtain Copies / Certified Copy of the Sanction Plan from BBMP.
The Bruhat Bengaluru Mahanagara Palike, is the administrative body responsible for civic amenities and some infrastructural assets of the Greater Bangalore Metropolitan Area. BBMP represents the Third Level of Government (the Central Government and State Government being the first two levels). It is run by a City Council composed of elected representatives, called "Corporators", one from each of the wards (localities) of the city. Hence it is a "Public Authority" under Section 2 (h) and under Section 2 (f), 2 (j) and Section 6 we can ask for the Certified Copy of the Sanction Plan of any building. For building with G4+ Floors the application must be made to the Town Planning Department of BBMP Head Office and below G4 Buildings application must be made to the concerned Town Planning Department of BBMP Zonal office.
Please visit https://onlinerti.com/ or https://onlinerti.com/how-to-file-rti-online-for-karnataka for further assistance.