es_US spanish locale doesn't recognize meridian (AM/PM)

Hi! I am working on a bilingual site for US users - it will be in English and Spanish... I came across some difficulties formatting dates. I set the locale depending on language chosen and use strftime to display the formatting I need. However, it looks like none of the Spanish locales (I am using es_US, but I tested others) use AM & PM values. I realize that AM & PM aren't used much outside US, but I believe that Spanish speaking users within the US will be more familiar with AM/PM notation. I looked at the source files for locales on the server (I am using Redhat Linux ES), and, indeed, values that relate to AM / PM are empty. I am not sure whether there's a PHP way around it, or maybe I should find a different source for the es_US locale and reinstall it (not sure how to do it), but so far I had no success finding any information about it... Seems like everybody else is perfectly happy using 24-hour format for US Spanish locale on Linux / Unix. I would appreciate any help! Thanks