Here's a few spots that sell the A Frames

Bronsons

https://bronsonshop.com/collections/new-arrivals/products/military-cotton-tank-top-olive?variant=43803591606488&mibextid=Zxz2cZ

Soldier of Fortune

https://www.sofmilitary.co.uk/ww2-vest-us-army-cotton-undershirt.html

At The Front (when they get back in stock)

https://www.atthefront.com/Reproduction-WWII-US-Army-tank-top-p/usustt.htm