Here's how the 13th Amendment was found:
In the winter of 1983, archival research expert David Dodge, and former Baltimore police investigator Tom Dunn, were searching for evidence of government corruption in public records stored in the Belfast Library on the coast of Maine. By chance, they discovered the library's oldest authentic copy of the Constitution of the United States (printed in 1825).
Both men were stunned to see this document included a 13th Amendment that no longer appears on current copies of the Constitution. Moreover, after studying the Amendment's language and historical context, they realized the principle intent of this "missing" 13th Amendment was to prohibit lawyers from serving in government.
So began a seven year, nationwide search for the truth surrounding the most bizarre Constitutional puzzle in American history -- the unlawful removal of a ratified Amendment from the Constitution of the United States. Since 1983, Dodge and Dunn have uncovered additional copies of the Constitution with the "missing" 13th Amendment printed in at least eighteen separate publications by ten different states and territories over four decades from 1822 to 1860. ...
Dodge and Dunn now went to the Library of Congress and were allowed access to the rare book room. There they found an un-cataloged book entitled "The Revised Code of the Laws of Virginia", 1819. The amendment was there, listed as the Thirteenth Article of the U.S. Constitution. This, of course, indicated that a 13th state had indeed ratified the amendment, constituting a 3/4 majority of the states of the Union at the time the amendment was proposed...
[link to w3f.com
I've had the above article in my files for over a year. I hope the link is still good.