Not sure about brokers, but I used American Express travel insurance a year or so ago as they were the only company I found who would cover my watch against accidental damage as well as theft when I went abroad.
try the ba exevutive club, they do great insurance, and its free to jion otherwise try trailfinders or travel bag the travel agents
last is hiscox they fo high value household insurance
very happy with their service even though i have not actually got a policy!
as above amex may also do a good job