Shortly after recovery efforts began at ground zero, New York City's mayor’s office started donating metal i-beam sections from the Towers to pretty much anyone who signed an affidavit agreeing not to profit from it and not to sue regarding any possible chemical contaminants.
More than 150 towns, fire departments, churches, and museums have received the steel pieces. The list includes three presidential museums; the city of Dodge City, Kansas; the Historical Center for Southeast New Mexico; a Texas firearms-training company; and a California light-rail advocacy group called Transportation Involves Everyone.
Walt Bigelow, a senior accountant in the finance office at Denver International Airport, got two girder sectionsn 2002. In the end, however, the airport’s managers decided against displaying them so Bigelow donated the larger section to the Denver Firefighters Museum, where it's currently on display. The other piece has been in Bigelow's office ever since. You could try contacting Mr. Bigelow regarding borrowing the piece, I suppose.
His Linkedin URL is http://www.linkedin.com/pub/walter-bigelow/0/80/583
Any other leftover pieces of the charred, burnt, and twisted steel from the Towers are under the watchful eye of the Port Authority of New York and New Jersey. A Kennedy Airport hangar is used to store the material. According to an article in last September's NJ.com, XXXXX XXXXX, a spokesperson for the Port Authority, said that, “People send us proposals for making use of or displaying the pieces, and the main requirement we have is it is used for some type of memorial or public display.” Each request also has to get approved by a federal judge or the FBI before it is released.
Numbers for the Port Authority are listed at http://www.panynj.gov/contact/contact-us.html
FYI eBay has a whole slew of twin Towers memorabilia which may be of further interest. Check it out at http://www.ebay.com/sch/i.html?_trksid=p4069.m570.l1313&_nkw=world+trade+center&_sacat=0
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