Snow Leopard = OS X 10.6.x
It is Not available as a download... It is a Paid Upgrade.
Do this first...
Check that your Mac meets the System Requirements for Snow Leopard...
Snow Leopard Tech Specs
If so Contact Apple in your Country to Purchase a Snow Leopard Disc...
In the US...
1-800-MY-APPLE or 1-800-676-2775
After the Successful Install, run Software Update to get the latest updates for Snow Leopard.
Be sure to make a Backup of your Current System Before Upgrading...
If you're using an iPad 2 or 3 that was updated to iOS 6, click here and download the software.
If you're using an iPad 4 or iPad mini and are on an Intel Mac, phone the online Apple Store and order a Mac OS X 10.6 DVD.
If you're using an iPad 4 or iPad mini and are on a PowerPC Mac, you can't.