frequency of using the same judge - Page 1

Can anyone tell me if there is a rule or guideline for how many times a Region or Club can or should use the SAME Judge in a given time frame? I am looking at the Region that I am in and seeing mostly two judges repeatedly called upon to judge conformation shows. Aren't there any other judges available? Are there only a few SV judges able to come to the United States? How often do you think any one judge should return to the same Region? The same Club? Just curious.