LIBERTY was a weekly features and fiction magazine that aimed at the mass market in American life and culture. It had some excellent material and art, but it was not aimed at the high end. It lasted from 1924 to 1950, and a nostalgia-oriented version was revived in the middle of the second half of the 20th century. Here's a page about the magazine that gives you a feel for the title.

Dorye Roettger's book Rivals of Rockwell has over 90 very-large-format, beautifully printed glossy illustrations from old LIBERTY covers (cropped to delete the logo, and sometimes a bit oddly) -- and it's not very expensive. After you've looked at the description of the book, you can find some issues on Amazon while you're there, but the best place to look for old issues of the magazine is eBay.