David, I just went through this. I really used a great deal of time to find the right coverage and a good price.
Just so you know, in the past (karate & kickboxing) I have used Markel and the Martial Arts group, which are probable well known for doing business with various systems. I found Fitness and Wellness to be the best bet for the aikido I'm doing now.
http://www.fitnessandwellness.com/si..._insurance.asp
Hope it helps.
Asim