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While what you were hoping to find does not exist in the way you stated it, the real information you want is available. Where? In your logs.
Your logs tell you what keywords were used to find you. The biggies are obvious ones that you are probably already tracking. But a site with a lot of information will have a few hundred keywords that, once in a while, trigger a hit. None provides a lot of traffic, but in the aggregate the hits add up.
You can extract them from your logs and periodically check where they rank. Putting some work into increasing their ranking will bring you a nice increase in traffic.
You may want to ask that question (if you get no replies here) in the Tracking and Logging [webmasterworld.com] forum. You will find it a very useful resource if you get serious about using your logs.
In his Successful Site in 12 Months with Google Alone [webmasterworld.com] post Brett writes:
K) Logging and Tracking:
Get a quality logger/tracker that can do justice to inbound referrals based on log files (don't use a lame graphic counter - you need the real deal). If your host doesn't support referrers, then back up and get a new host. You can't run a modern site without full referrals available 24x7x365 in real time.
The reason for this is quite simple. If there is some keyword that I _should_ be using but don't _know_ I should be using, I'm not going to place well (if at all) in the SERP's for that keyword and consequently, no one is going to be placing that keyword in my log (because no one is getting to my site based on that keyword).