I have seen the books and decals affixed on many 1970 E-bodies that were in California.
I believe that the state of California issued these in or around 1971/72 as a method of reducing smog on the 1970 and earlier model year cars.

If I recall there was also a decal placed on the valve cover of the engine stating the NOx reduction as well.

Definately not Factory installed! but a cool piece of memorabilia

I have not seen anyone actually selling the books lately - you might try one of the "car book" places in CA that specalize in older factory manuals. They are often at many of the multi car make shows or online.