How do I get a copy of Mac osx Lion?

And just in case you were asking about Mountain Lion...

Mac OS X 10.8 Mountain Lion installer download:

https://support.apple.com/kb/DL2076?viewlocale=en_US&locale=en_US

EDIT - I suggest you use only Safari to retrieve either of these downloads. Firefox or others may not work.

Mac OS X 10.7 Lion installer download:

https://support.apple.com/kb/DL2077?viewlocale=en_US&locale=en_US