These are some 3 year Diploma Colleges for Architecture in Mumbai:

• Rizvi College of Architecture, Bandra
• Vivekanand Education Society's College of Architecture
• MET Bhujbal Knowledge City, Nashik
• BVCA Pune - Bharati Vidyapeeth College of Architecture

You can check the complete list of diploma colleges for architecture in Mumbai from here - https://engineering.careers360.com/colleges/list-of-diploma-in-architecture-engineering-colleges-in-maharashtra