Aaach yes, welcome to travel hell. Curious for tips as well. More and more starting to look at local diving, no matter how cold it is, or driving/taking a train, at least within Europe. Air travel has become such a pain nowadays.
I have more or less given up. Granted I am in a different market (Europe) but basically finding absolute nothing. Ridiculously low limits (like 1500 Euro), coupled with low per item limit (like 300-600) with statements like "camera and all lenses" counts as one item. And literally every single insurance has a small print "if you put valuables (and yes, camera or funky dive gear will count as this!) in hold, it invalidates the cover". Home insurance only covers when "at home away from home" (so say a hotel) but not in travel.
There is an insurance if you are a pro (business) but being private, you are screwed mostly.
Airlines are not better - there used to be an option for extra insurance on some, now it seems a dead concept. And more and more becoming absolutely strict about hand luggage with limits being a joke - 7kg is a norm now (I am jelly about Air Canada, boy that 23kg is a dream) . And trying to reason with them on the grounds of valuable/delicate etc. is a complete nonsense - even the "reputable" ones here answers are "stop being poor and book business" (though even there allowance starts to be puny compared to what is was)
And don't expect much help from the airlines when the bag vanishes into thin air . Speaking from an experience - whole bag of dive stuff including week old air freshener, poof and gone. Hence stuffing those with AirTags now (the only good thing about icraphone), and hope that at least I can track it then.