Member David Lindwall's article
got Guatemala? was published in
the March 2019 issue of
The American Philatelist. APS members
may read the article online here.
The March/April issue of Topical Time,
the journal of the Americal Topical
Association, contains two articles on
Mayan topics on stamps.
HR Harmer Auctions, Sale 3033, August 6, 2020 has ten (10) Guatemala stamp and postal history lots in their current auction.
Their main website:
Here is the search that should get you to the Guatemala collections: