On Linux shared hosting accounts you can find the default system php.ini and php5.ini files here:
php.ini applies when running php4, and php5.ini applies when running php5.
You will not be able to get to these files via FTP, but you can via SSH.
If your account does not have the ability to use SSH, you could write a simple php script to print out the contents of the files to a web browser, for example:
upload a file called 'showme.php' to your account in your main website directory with the contents:
<? system("cat /web/conf/php5.ini"); ?>
Then hit this page with a browser, eg: http://yoursite.com/showme.php
Now you can cut'n'paste the output to your custom php5.ini file with your own changes appended.
my current php config Download HERE 2013v2