I am not finding the right pneumatic actuator though, which if I did, giving it an air supply would not be an issue.
There are plenty of ways to homebrew a pneumatic actuator from parts you can find in the plumbing section of your local hardware store. Seriously, it's fairly easy.
What's more difficult (and potentially expensive) is the control section - pneumatic control solenoid valves don't tend to be cheap. Also - if you need position sensing, you would need to build that in as well. But the control issue is one that would still be an issue if you went with commercial pneumatic cylinders.
As far as commercial cylinders are concerned - a great and long-running brand is Bimba Manufacturing:http://www.bimba.com/
...they've been around seemingly forever.
You can typically find their stuff surplus at various vendors as well (though if you need a specific size for a given application, going directly to them is the best option - though not necessarily the cheapest).