Can an international student gain admission to medical school in the USA?
According to the Association of American Medical Colleges (AAMC), in 2013, 1,088 of 48,014 applicants to U.S. medical schools in 2013 were not residents of the U.S. Of these, 115 matriculated (10.6%, compared to 41.8% of applicants overall).

So it is possible to gain admission to medical school in the U.S. as an international student; however, it is more difficult since (as you have noted), there is a very small number of schools that will admit international students.

The National Association of Advisors for the Health Professions has an article, "Medical School Admission Policies Towards Non-US Citizens", that lists all the medical schools in the United States and their policies on accepting international students, as well information on how many international students they have accepted historically. While it's a bit dated (from 2008), you should still find it helpful as a starting point. For example, it points out that George Washington University has an M.D. program specifically for international students.

Note that international students are generally not eligible for federal aid, which can make it very expensive to pursue a medical degree in the United States. Many schools will require applicants to submit documentation showing that they will be able to fulfill their financial obligations to the school if they matriculate.