Unfortunately, if your 18+ Oyster card has been lost, damaged or stolen, the university is not able to replace it for you.
However, you can order a replacement card from Transport for London (TfL) directly. Visit the TfL lost, stolen or damaged Oyster photo card webpage for information on ordering your replacement, and on possible admin fees.
If you think you have lost your Oyster card on campus, it is always a good idea to visit the Student Centre or other receptions on campus to see if the card was handed in.