There are boots to fit -- follow the advice by Modgirl, Suz and others. Don't worry so much about "medium" or "large" calves, as long as they are proportional to your overall shape (what others above had said). The question is buying the appropriate fitting items -- some are cut too narrow, and most people could not wear them.
I know the boot buying frustration. I am very picky about the styles of the knee boots I like so I didn't try 40, but I tried several that didn't fit and finally found 2 over the last 5 years that did fit and that I really liked. My problem now is that since I have gained a lot of weight, I also gained about 2 to 3 inches on my calves and my boots didn't fit this past winter (couldn't zip them up past the calf area). Boy was I bummed, but I didn't want to shop for new knee boots (cost prohibitive too). Of all the things I missed wearing, this was my most missed.
@Suzanne: 4'11" = 147.5cm; 14" = 35cm; 15 = 37.5cm.
