Go to CCS, and Reports>Staffing.
Pick a base, fleet, and seat. You can see how many guys, and what seniority, are there.
It does NOT show potential incoming/outgoing though, such as through bids, bumps, new hires, etc.
No way I know of to show how many jets per base.
Under PBS, you can find how many pairings there are per bid month, by base, by fleet. That would give a good approximation.
Changing subjects:
The company has issued two separate reports on the 777-300 rumor saying "....it is an option, but we plan no incremental fleet growth...."
Given the veracity of their denial, it must mean they are buying them as we speak.