The app store is the only place to get apps for your iPad. Some developers allow you to download older compatible versions of their apps - if there is a free game that you want then you could try downloading the current version on your computer's iTunes so that it's in your account's purchase/download history, and then on your iPad see if you can download an older compatible version of it. If it's a paid-for app then try contacting the developer first (there should be a link to the developer's site on the app's description page) and ask them if that will work for their app (don't buy it first and then find that it doesn't).
Or see if this page helps : https://sites.google.com/site/appleclubfhs/support/advice-and-articles/finding-a pps-for-older-devices