We were not able to find this clip, or even if it was recorded. Your question informed us of the need for a comprehensive list of audio archives and other resources. We are going to compile a list of these resources, but until then, here are some suggestions from our librarians.
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Television news archive at Vanderbilt - http://tvnews.vanderbilt.edu/
Perhaps the Museum of Film and Television?
Try also contacting the news library at the organisation that broadcast the clip you're looking for. Most news organisations have their own archiving service, and many can arrange to dub the clip you are seeking for a fee (as long as they own the copyright to make copies of course). SLA News division: http://www.ibiblio.org/slanews/
If it's related to politics, try the equivalent of a parliamentary library (a congressional library? I'm not sure of the system over there). Many libraries of that type archive news bulletins.
Most libraries that are not attached to a news organisation generally don't archive news clips as they can't get licensing for it. I worked in a news library for 5 years and faced these roadblocks often ("I need a clip of such-and-such saying X etc").
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Don't know if these are of any value:
http://www.freepint.com/gary/audio.htm
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I hope no one's said this yet (my inbox is unruly), but there's the subscription database World News Connection (http://wnc.fedworld.gov/).
I used this when I went to school/worked at McGill, and I remember it also having American content (I could be wrong). Their website indicates that it's only non-U.S. sources. And I think this is just transcripts, not actual audio clips.
