I need to upgrade my MacBook Pro from 10.6.8 to 10.7 but can't find it anywhere

Before purchasing Lion make sure your Mac can run v10.7 Lion > System requirements for OS X Lion and Mac OS X v10.6 - Apple Support

You can purchase v10.7 Lion here > http://www.apple.com/shop/product/D6106Z/A/os-x-lion?fnode=e26d3801614181e465158 ae0b8d89b1a4a3e27464298bbc95391747e57e0e…

After purchasing you should receive an email notification with a code to redeem at the App Store so you can download Lion from there.

Open the App Store then select Redeem on the right under Quick Links.

What model MacBook Pro?

Lion is a paid update and is no longer supported by Apple.

You may be able to go to either El Capitan or even Sierra