While this will not help you now, the process below could help for future requests.
In our environment ESP is recycled weekly.
We set up a job to execute the ESPCOM DEST(-) command shortly before the recycle.
The information is written to a data set with the following name:<HLQ>.<ESP Subsys>.AGENTS.DYYMMDD.THHMMSS
This creates a weekly snapshot of what agents are used.
After running for a period of time you can use the SRCHFOR <Agent Name> to locate the data sets it is in, which will show what week the agent was no longer used.