You'd be best off checking out the United board and the Mileage Run board.

Read the Primer on Mileage Runs.

Then, after reading through archives, you may want to post in the Mileage Run thread.

Give your specific dates of availability.

Give a price range -- the most you'd be willing to spend.

Give the exact number of miles you need.

If you get lucky, tvl4free might even answer.

Of course, the easiest way to get 18,000 miles in one shot is a SIN run. Please see:
http://www.flyertalk.com/forum/Forum81/HTML/002294.html
http://www.flyertalk.com/forum/Forum...ML/001935.html
http://www.flyertalk.com/forum/Forum...ML/002059.html
http://www.flyertalk.com/forum/Forum...ML/002110.html
http://www.flyertalk.com/forum/Forum...ML/002168.html
http://www.flyertalk.com/forum/Forum...ML/002293.html
http://www.flyertalk.com/forum/Forum...ML/002763.html
http://www.flyertalk.com/forum/Forum...ML/002806.html
And many, many more...

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