They do show up on eBay from time to time. Try a search for “bank vault” and/or “vault door”. However, often the prices they ask are outrageous, especially considering the very great cost to the buyer to uninstall and move one of these doors. If they really want to get rid of a door, they should be paying you to take it off their hands. I wouldn’t expect to find and move one of these for less than around $30,000.
If you do a Google search for “vault door for sale” (without the quotes) you might get a few interesting hits.
There is an Apple Bank in New York (2526 Grand Concourse, The Bronx, or maybe it is an Emigrant Bank) that is about to close in less than a month (mid-November 2014 per their web site which I now cannot find). They did list their Diebold doors for sale on eBay but I didn’t follow the auctions so I don’t know if they sold. Here is one of the images:
