I would recommend that you contact the school you attended and see if they or the district still keep diploma records for the year you graduated. If the school you attended is in the United States, you can use SchoolFinder to find their contact info:
I think it is fairly unlikely that your school will be able to help you with this. A friend tried to do this a while back, and while the years are different, the time that had passed was similar. The high school basically said "no way."
So it depends on what you want the diploma for. If it is just for a memento or to hang on your wall (as it was for my friend) then look up a classmate who graduated the same year, scan his or her diploma, and use Photoshop (or find someone who can do this step for you) to "fix" the name. If you're a professional and the diploma means something to clients, then it would be wise to affix a small label to it "reconstruction of the lost original"
The "official transcript" is the real record of your attendance and completion and performance. The diploma isn't (usually) thought of as an official or legal document. As long as you're not using it to represent yourself fraudulently, then recreating the diploma in the way I described might serve your purpose.