In PHP you could do something like:
header( 'Location: http://www.yoursite.com/index'.$i.'.html' ) ;
This allows for 10 index files: index0.html to index9.html. It is not strictly random, as it increments at one second intervals from 0 to 9 then back to 0.
Note: That code MUST be at the very start of the file, which MUST be named '.php', E.g. 'index.php'.