If you can't find your copy of the license, you have two options:
1. If it was fairly recent (since the late 60s), you can get a license verification letter from the FCC. In some cases, they may require you to pay for research fees from their records contractor. Information on the "License Verification Letter" can be found in an ARRL web site article at
http://www.arrl.org/news/restructuring/faq.htmlitem number 6. Note that since this was published three years ago, the FCC has changed records contractors. The new company is Qualex, and their phone number is 202-863-2893.
2. If you don't need the exact date, but can accept something rougher, you can pinpoint at least the year of issue by looking in old callbooks and finding out when you were first listed. If you need this data for license credit, callbook listings are now accepted by VEs. Contact me directly if you'd like help in this are.
73,
Steve
W3HF(a)arrl.net