Supposedly the Sidi Force is the way to go. It has an adjustable plate that allows you to expand the boot in the calf area. Check the DRN TESTED pages. Rich and Okie did reviews on it. I know that the AXO RC-5 isn't very good in that area. I've only got 17" calves, but I wear braces and they won't cut it.:(
The Alpinestars Vector boots are worth considering if you are comfortable with a softer style boot. It uses a velcro closure at the calf that has enough adjustability to fit my calves and CTI brace. So far it's the only full length boot I've found that wiull accomplish this.
Eric Gorr is doing a general review on the Vectors which should be posted shortly.
Sidi has a shorter boot called the Discovery that might solve the problem by not going so far up your calf. It may be to much of a light duty boot for your use. http://www.motonation.com/trialzero.cfm
Tomuch...I currently use the SIDI boot. I am a personal trainer by trade, and therefore lift weights daily. I returned the Delta Force after only a couple hours of riding. I really liked the boot, but found the plastic WAY to soft - serious scuffing and scarring. So I went with the next level down, with the tougher boot, and traditional soul, and have been very happy with them. My first pair of SIDIs lasted almost eight years!
I also have this problem. I finally broke down and purchased a pair to Tech8's. They are OK, but I am on the last notch for the second and third buckle in the middle of the boot. They finally got smart and lengthened the top strap, but forgot about the others.