A long time ago in a galaxy far, far away...
OK, back in May 2012, right here on Earth, I posted about the 1936 Arkansas Statehood Centennial-Joseph Robinson half dollar and included images of the coin's original holder/mailer that I have in my collection. For some reason, I didn't post the envelope used by Stack's of New York to send the coins to its mail order buyers. I noticed the omission this evening (Who says I'm not on top of things?!

), and decided to "complete" the original post. (A link to the original is found below.)
As can be seen, the envelope is not one that was custom printed with designs that matched the coin; it's just a readily-available, standard envelope that was purchased from the United States Envelope Company. It does, however, appear to have been pre-printed with the Stack's return address; the "Contains Merchandise" and "INSURED" blocks also appear to have been added. (Speaking from experience, it's a common practice to use a local printer to personalize standard envelopes that can be purchased in bulk.) I suggest that the envelope was used by Stack's to mail out a variety of coins to its customers, not just the Arkansas-Robinson coin.
In late 1936, Stack's advertised that they were appointed as the "Sole Distributors" of the coin and that they would be ready for distribution by December 31, 1936. Per contemporary reports, however, distribution of the coins did not begin until early February 1937. As the envelope shown features a "Feb(ruary) 2, 1937" postmark, it would seem that the coins it contained were among the early purchases of the half dollar.
I used the plural "coins" above based on the 13 cents worth of stamps on the envelope. In 1937, the Domestic Letter Rate was three cents per ounce; even with the cost of insurance added in, the affixed postage would allow for the holder/mailer to be filled with four or five coins.
1936 Arkansas-Robinson Mailing Envelope
FYI: Mountain Lake still exists today - it is a private community built around a golf course; its history dates to 1916. 
If you'd like to read my original post, you can find it here:
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1936 Arkansas Statehood Centennial - Joseph RobinsonFor other of my posts about commemorative coin and medals, check out:
Commems Collection.