No need to worry. If your HO doesn't cover then AMA takes up the slack. Let the sharks fight it out among themselves.
That's not necessarily good news.
My Personal Liability insurance policy covers me for liability 'not covered by any other policies held by the insured party'. The 3rd party liabilty insurance offered by our national modelers' association has a similar caveat.
In such cases, insurance companies have been known to fight for years, without paying a single dime until the matter was settled.