After I retired from the Air Force, I got started a Federal Civil Service Career.
Anyway, I was working as a Federal Civil Service when the Official Mail Stamps were in use. I had my secretary save all the Official Mail envelopes that came in. I ended up with a nice sized box of envelopes.
Here are two from the box addressed to me, interesting to have modern postal history with my name on them.
As I remember some where in the box is a $5.00 Official Mail stamp on a piece (from a heavy box), will try to find it and post it in a day or two if I can still find it.