How can one find old archived issues of LEGO Mania Magazine?
There is currently one public library in the WorldCat system that has cataloged LEGO Mania Magazine, but it does not have it available in digital form. 

Other LEGO Club magazine titles have been collected by some WorldCat system libraries, including:

Brickmaster Magazine

LEGO Club Magazine

LEGO Magazine

None of these titles appear to be available in digital format from any WorldCat libraries at this time.