I'm a little late to the conversation and I think it's all been pretty well said.
KCBS has the most thorough judge curriculum with MBN probably second by a ways. There are a few other sanctioning bodies but they don't have very many contests. KCBS has hundreds running almost all the time with the bulk running all Saturdays from April through October.
Judging is an interesting, consuming avocation if you get into it. Really good judges are always needed and appreciated by contest organizers. I view judging very much like a "practice" similar to one approaching law, medicine or consulting. You'll never get it perfect but the challenge is extremely satisfying and rewarding for those who apply themselves to it.
I cook and judge and love both. Saying that the two efforts compliment each other is an understatement. Keep trying to find a class that fits your schedule. Also, check the schedule on the website (kcbs.us) often because new classes pop up from time to time.
Hub