I've looked, I've really looked... and I can't find one anywhere on my system. Depending on whose documentation you read, it could be in any number of directories, but I can't find it.
Anyway, Apache and PHP are running fine on my system. What I want to do is increase the max_execution_time so that a script I run to process a ginormous amount of text has enough time to complete.
The PHP installation on OS X does not come with a php.ini file by default (which is why you can't find one). Download the PHP source code for your version of PHP and copy its php.ini file to /usr/local/lib. Then restart Apache.
Larry