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You can file it online at the United States Patent and Trademark office
Here is a link to the process http://www.uspto.gov/trademarks/process/index.jsp
And here is the link to the part of the website where you download the form http://www.uspto.gov/trademarks/teas/index.jsp
This is the actual government website that monitors and regulates Patents and Trademarks in the US.
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