You need the account passcode for each SETI account, which is a nonsense sequence of letters and numbers. At some point, this was hopefully sent to each of the emails in question. If you still have your inbox archived from those periods, you may be able to search up the passcodes.
If you do not have the passcodes (no inbox archive, or passcode never sent), then the only real hope is to temporarily reactivate the emails in question. If the emails were with a major service like Earthlink, it is common for them to reserve previous users and not reissue the address. Ask for it back for a month - this will cost a few bux.
If the emails were in a company mail domain, the only real way is to ask a friend still working there to reclaim your old address, then have Berkeley
send the passcode.