Here is a link with some general info on dog bite laws, and towards the bottom there are few agents listed that may be of interest to you (if you cant find a "normal" policy that will give you proper coverage).
DOG BITE LAW - Insurance for the Dog Owner
Keep in mind that every company may have different guidelines in place for different states. so if Travelers (for example) gives you coverage for a GSD in Texas, they may not offer it in Florida.
it sucks that its getting to the point where people may not be able to get insurance because of their beloved pet, but there are more and more restrictions in insurance now in general. trampolines being a new "big issue".