Scalability is recognized as a primary factor to be considered in the design of distributed systems. The scalability of object-oriented middleware CORBA becomes a major concern as it has emerged as a standard architecture for distributed object computing. In this paper, a systematic scalability analysis of the basic components of CORBA specification is attempted. From this analysis, Portable Object Adapter (POA) and Implementation Repository (IR) are identified to influence scale of the CORBA based system. The specification of POA provides enough flexibility for the application designer to handle scalability. The existing implementations of IR have a trade off between scalability and object migration. A scalable design of the IR is proposed which allows individual objects to migrate without compromising scalability. A performance comparison of the proposed model with the existing IR designs is made using a simulation study.