Have you tried contacting the webmaster of unitedforpeace.org and asking him/her if the calendar was a freeware script?
Alternatively, you may try searching places like HotScripts or simply writing your own. Really, it wouldn't take much to write your own event script as you're talking about, since there's really no visual "calendar" involved. All you'd do is input events and dates (use [man]strtotime/man to generate a Unix timestamp and store the integer) into a SQL database, and run a query like so:
SELECT `eventName`, `eventDescription`, `eventTime` FROM `events` WHERE `eventTime` >= UNIX_TIMESTAMP() LIMIT 10