You could have downloaded USInternational 1.2 for Mac from our application library for free. The application lies within System Tools, more precisely General. This free Mac app is a product of Rainer Brockerhoff.
From the developer:
USInternational... Many international users have keyboards with the U.S. layout, and are accustomed to typing accented characters with the key sequences of the Windows "U.S. - International" keyboard layout. They often don't wish to get used to the Mac's option-key sequences for accented characters, and many mistakenly complain that "the Mac doesn't allow accented characters at all".