Go to www.pubmed.gov. This website is a compilation of publications from various scientists in various fields. It is updated somewhat regularly and has records going back for many years.
Type in the subject or field in which you are looking for a U.S. scientist. The publication results pulled up will offer a wide array of authors. It is also possible to search by the scientist's name, if known; the search engine will pull up any publications for that person.
Browse through the search engine choices. Below the article title for each choice are the authors' names. Click on any interesting title link to view the abstract for the article. The abstract is a summary of what the article is about. Right below the title and author names are the university, city, state, and/or country those scientists reside in. Simply find an article where the scientists are located in the U.S.
Perform a Google or Yahoo search for the university listed on the abstract. Click on the link for the university and type in the scientist's name in the search box. One of the links pulled up should either lead to the scientist's webpage (which would list research interests and possibly contact info), or the department the scientist is located in. If the user clicks on the department link, there should be contact information for the department administration. It should be possible to call them and find more information about the scientist in question or to make an appointment with that scientist.