Found ECFMG report with the match results for both US-IMGs and international IMGs. More than half of US-IMGs applicants don't match. It does not say what fraction of fresh graduates do not match: there could be many repeated applicants, not matching year after year and inflating the total number of applicants. Still, I think, the report might be useful to those, contemplating studies abroad, as it provides firm numbers to ponder on.
http://www.ecfmg.org/echo/imgs-2012-match.pdf
"In 2012, The Match experienced record high numbers for both first-year positions offered and total active applicants 24,034 and 31,355 respectively.
Of the 4,279 U.S. citizen IMGswho participated in this Match, 2,102 (49.1%) were matched to first-year positions; this was the ninth consecutive year
that the number of U.S. IMGs matching to first-year positions increased. Of the 6,828 non-U.S. citizen IMG participants, 2,775 (40.6%) obtained first-year
positions; this marked an increase over 2011, after declines in the two previous years"
http://www.ecfmg.org/echo/imgs-2012-match.pdf
"In 2012, The Match experienced record high numbers for both first-year positions offered and total active applicants 24,034 and 31,355 respectively.
Of the 4,279 U.S. citizen IMGswho participated in this Match, 2,102 (49.1%) were matched to first-year positions; this was the ninth consecutive year
that the number of U.S. IMGs matching to first-year positions increased. Of the 6,828 non-U.S. citizen IMG participants, 2,775 (40.6%) obtained first-year
positions; this marked an increase over 2011, after declines in the two previous years"