Okay, found the office envelope (kind of). They're called " 3/4 flap document wallets." They also make 1/2 flap and full flap versions. I believe they used the 3/4 flap version for the film. They are way easier to get in the UK than in the US. Which makes sense because Barry Gibbs was the property master for The First Avenger.
Color matching has been a bit of a challenge. The prop looks kind of OD green, kind of aged manilla. I'm not sure what it is. And the product images where I can find them are also inconsistent. A UK company called Exacompta makes them in a color called "buff." Some of the pictures match, others don't:
https://www.amazon.co.uk/Exacompta-PW5-BUFZ-Guildhall-Protection-Heavyweight/dp/B00BI590KM
I found a company called Whitebox in the US that makes a yellow. Again, in some images the colors match. In others, not so much:
Amazon.com
At any rate, a maker interested in this would have to add their own string closure. Easy enough if you get some dark red card stock circles, brass brads, and white string.
