Updates on Kellogg's Factory Sets - Anyone?

I still don't see factory sealed sets from 1970 - 1978 much on ebay.   Where else should I look?  At card shows I rarely see any kind of Kellogg's sets.

The envelope pictured below once held a factory set but now it just hold some of the panels.  I've gotten a few like this after some decided to sell and/or grade the best panels in the set.

Where does one factory sets besides 1970 Rold Gold, 1973 Kellogg's Baseball and 1979 - 1983.  The last five years are easy to find and quite affordable if you look around.

I don't even know what a factory set looks like from 1972, 1974 - 1976.  Are they just envelopes like the one above or are they the envelope inside the box like the newer sets?