Step 1: Identify the external source of recruitment in the case.
Vista Bank did not directly advertise for or screen candidates itself. Instead, it approached Avon Consultants, a professional third-party firm, to find middle-level managers. This points to a specific external recruitment source.
Step 2: Name the source.
The external source of recruitment used here is Placement Agencies and Management Consultants.
Step 3: Explain Placement Agencies.
Placement agencies are specialist firms that match supply and demand for skilled human resources across a wide geographic area, often at a national level. They maintain large databases of qualified candidates across many industries and job functions.
Step 4: Explain Management Consultants.
Management consultancy firms go a step further by specifically helping client organizations recruit technical, professional, and managerial-level personnel. They typically advertise positions on behalf of the client (sometimes under their own name for confidentiality), tap their proprietary databases of professionals, conduct initial screening rounds, and then forward only a well-curated shortlist of candidates to the hiring company.
Step 5: Connect to the case.
Avon Consultants advertised on job portals under their own name, accessed their database of experienced professionals across India, conducted extensive screening, and then forwarded a shortlist to Vista Bank - precisely how a management consultancy operates.
Step 6: Conclude.
The external source of recruitment in the case is Placement Agencies and Management Consultants, represented here by Avon Consultants handling the recruitment of middle-level managers for Vista Bank.
\[ \boxed{ \text{External source: Placement Agencies and Management Consultants (Avon Consultants)} } \]