I do not think the original degree diploma can be replaced. However, you can apply for an "Award Certification Letter" and a "Transcript of Studies" at the Admissions, Registration and Records Office as written proofs of the degree that was conferred.
2007-02-10 07:48:22 補充:
Additionally, you may apply for a 'Testimonial' at the ARR Office as a written proof of your course completion and award of the degree as well.