The harp owner typically has several avenues to pursue to obtain insurance coverage for their instrument(s).
For non-professional players, their home-owner's or tenant's policy can often be amended to include coverage for specific musical instruments. These policies will exclude losses associated with professional engagements and also may not cover the instrument while traveling. You will have to read your policy carefully (oh joy of joys!). If you call your insurance agent and the response is something like "Oh, I think that's covered most of the time" - you need a new insurance agent, that's for sure!
Professional players will want to research the harp insurance recommended by the American Harp Society or the American String Teacher's Association. These two national non-profit organizations have worked with the insurance industry to develop group policies that are both affordable - and, more importantly - provide genuine all-risk coverage. Of course, even these policies have exclusions - like leaving your harp unattended on a busy street corner while you grab a latté - but they are what most professionals use.