I am looking to get the following -

Basic code review to make sure they follow the guidelines imposed. Security code analysis to make sure there are no loopholes. No performance bottlenecks by doing a load test etc.

We have lot of code coming in from third parties and is becoming laborious to manage code reviews and hence looking to see if others employ such practices.

I understand that it may be a concern for some and would raise the question "Well, who is going to make sure the agency is doing their job right?" But basically I am just looking for a third party who can hold all vendor code to the same standards.