Page not found original page in zen-cart

I have a script that logs page visits on my zen-cart site at the end of every page. Lately, I have been noticing a lot of hits to the page_not_found page. I am trying to retrace the steps to figure out what page(s) the visi开发者_StackOverflowtors are trying to go to, but with minimal luck. Is there someway to get the page and $_GET variables that were originally requested that triggered the page_not_found in zen-cart using PHP? I tried using the variables in the $_SERVER variable, but they return index.php for $_SERVER['SCRIPT_FILENAME'], and main_page=page_not_found for the $_SERVER['QUERY_STRING'] for the URI. For instance, is there some alternate variable to $_SERVER that zen-cart sets that contains the original parameters?

It's overwritten in includes/init_includes/init_sanitize.php line 125

$_GET['main_page'] = 'page_not_found';

You could save this value off and refer to it later in your logging.