Have you tried to contact the dose manufacturer directly? Give a Canberra or IPL a call and they may have the information you need. They can probably give the birth certificate on the source if it is one they made and that should have info like manufacture date, emission rate for beta and neutron sources or AKR for gamma sources.
If it is being shipped to you special form, then you may get this certificate as documentation. Or you could request the original user to send what he has.