Where can I get pages for 2011 MacBook Pro

Have you ever installed Pages v5 or later through the Mac App Store before? If you haven't then you cannot get Pages v8.1 for macOS High Sierra, which was the last compatible version for that operating system, and you would need to use Pages for iCloud, or a different word processing solution.

If you did install Pages v5 or later from the Mac App Store, you can launch that store again using the same Apple ID as used previously to install Pages. Press the option key while clicking on the Purchased tab. You should see Pages on that panel with an Update button which you would click. A dialog should appear offering to install the last compatible version of Pages (v8.1), and you agree to that.

If you cannot get Pages v8.1 for High Sierra, and if you do have the retail iWork '09 DVD, you could install that and then apply the iWork 9.3 Update which updates to Pages '09 v4.3, Numbers '09 v2.3, and Keynote '09 v5.3. These were the last versions available for that suite of applications, and they cannot open newer Pages document formats created after Oct 2013.

Do you still have the old macOS DVD Installer that came with the MacBook Pro?

What version of macOS are your currently running on the MacBook? It's not certain at all that Pages will work under a recent macOS. If you're running Lion or Mountain Lion you will will need Pages 4.1 or 4.2 respectively. Pages 4.x was part of iWork '09.