Proof of ownership is what most will ask for these days and that can range from receipts, bank/credit card statements showing purchase through to box it came in, instruction manuals, or photos of the kit. Each insurer is different. When you're talking to whoever you decide to approach, have a chat with them and ask what they would take as proof in the event of a claim. If they insist on receipts and you don't have them, move on. Even if they're the cheapest, if you can't provide receipts then you won't get paid which means your insurance is a waste of money.
As for which companies to try, depends what you're doing with your kit. If your just a hobbyist, you may want to try your house insurer. If your a working tog getting paid for whatever it is you shoot, then you'll need to speak to one of the specialists. There's many a thread on here about who to go to. Flavour of the moment seems to be Cliik.
