Even if FIRST itself doesn't keep a definitive tally on those statistics, perhaps your own team could keep a personal log about these things for any questions your sponsors may have? Our team started tracking that the year after I (and half of our team) graduated, and used to keep that data on our website (not sure if it's still there -- it's being remodelled right now). Sponsors and school board representatives really like seeing where these students end up, and it's a good way of maintaining strong alumni relations.
On a side note, I'm currently going to the same university as one of your team's alumni. He actually lives in the same residence hall as I do, too. He's currently enrolled in the robotics program and doing very well, currently a Junior. He and I both went with a group on a trip to the AUTOMATE conference in Chicago. It was a really cool experience and great for networking...