This website has 11 Narrow. I own the same pair, actually. I normally wear 11.5 Regular. The 11 Narrow do just fine for me, but I don’t wear them on a daily basis. https://armysurpluswarehouse.com/jungle-boot/
If you are a size 11 same as me you can fit an 11, and a 12 narrow fits me perfect and my feet are size 11 wide.
If theye dont have your size, you can go up a size. A 12 narrow will fit like an 11 reg etc