Try a dedicated photo insurance
Try getting an insurance that specialises in photographic gear. You'll find addresses in your country's photo magazines – i.e. for the UK, the BJP magazine or Amateur Photographer. Or ask in a local camera shop that specialises in pro gear (i.e. Calumet or Flash Centre).
I've got my insurance in Germany (my home country). It costs me 3% of the camera value each year, and it insures everything at any time, even in my car. (Between 0800 and 2200 that is – though, if I can prove I had an assignment where the gear had to be in the car overnight, i.e. a festival over the weekend, it is insured overnight. In case of theft, I'd have to get a witness to verify I was using my gear for a commission on that location)