I am assuming that you looked for the VIN on the horns of the frame. If not, check there. If you find a number, you can buy a VIN placard from Pangolin 4X4. If you do this, you can just have it stamped with the correct VIN.
Even if you can't find the number on the frame horn, you can do what someone suggested above, and get it through records. Once you get the original VIN, then buy a VIN placard and get it stamped. This is in keeping with the spirit of honesty and originality.
Hope this helps.
Gary
"I can't believe I'm sitting here, completely surrounded by no beer!" -Onslow