This fall I was looking for a plain olive cap and I couldn’t find one on the #menswear market. So I ordered one custom from the venerable Ebbets Field Flannels. Except you can’t really custom order just one, so I ordered a small run, and now they’re available.
Ebbets made-in-USA five-panel camp cap, all olive wool, white cotton band, white satin seam tape. Adjustable with leather/clasp closure. $39 + shipping in the United States.