Bill,
There is a company called backeast that will make a new tag if all the proper hoops are jumped through. Here is their link:
http://www.datatags.com/
The will require a letter from a law enforcement officer in your state attesting that the VIN # on the frame or block match the VIN on the title that you are having a plate made to match. You will need to supply a copy of the title as well.
Most states have a process as well, but they will issue an entire new VIN and usually a real ugly plate to go with it. I would not let your state even know that the tag is lost or they may impound the car and force the change to the state issued VIN!
:seeya