If you haven't seen this yet, unz.org has a huge online library of materials all the way back to the 1840s including periodicals and articles, books and films.

I tried a few Heinlein searches and turned up a number of interesting items including:

"Science Fiction Hawks and Doves: Whose Future Will You Buy?" from Ramparts magazine, Feb. 1972:
http://www.unz.org/Pub/Ramparts-1972feb-00025

A critical review of Time Enough for Love by John J. Pierce in Reason magazine, Septmeber 1973
http://www.unz.org/Pub/Reason-1973sep-00024

"They" in the original publication in Unknown, April 1941.
http://www.unz.org/Pub/Unknown-1941apr-00084

There is a lot of other material that I haven't had a chance to look into yet--you might give it a try (even for subjects other than Heinlein!) at unz.org.

Been there, done that. (Well, some of it, anyways.)

If you are into online full text databases, see this -- and let me know of any I should add.

Bill, thanks. I didn't realize that I was duplicating your earlier post.

I think you may have hit all the stories; there are some reviews and other material that mentions RAH there also that I'm going through now. Searching around is fun!