I am doing an adventure cruise in Alaska in June where we will be doing Zodiac landings and kayaking in the ocean. The tour company REQUIRES knee-high waterproof boots or I will not be allowed to do the Zodiacs (they want to prevent hypothermia).

Problem: I cannot find anywhere boots with a big enough calf circumference. Bare-skinned I need 18 inches (I have super big calves and cannot ever find fashion boots that fit) and with socks and tucked in pants, would probably need 19 or 20. I wear women's size 10 shoes; men's boots, like women's are proportional in the shaft, so to get this big of a calf circumference, I would need size 15 or 16 men's boots (I wear an 8 in men's).

I have looked at every boot on Amazon and Zappos; REI; Cabela's; Gander Mountain. Etc. Most sites list "wide circumference" as being 16 inches.

So, am I looking for a non-existent product? Any suggestions? Or should I just resign myself to being unable to do the Zodiac landings (which is actually OK as I am terrified to do this.) Thanks.