Put it on your house contents policy. A good company will give you "new for old" all risks. I use Aviva currently. When I had a major RTC they paid out £7000 in ten days.
THIS.
Some of the best advice I was ever given was only ever to buy Defaqto 5* insurance. The rating covers their payout terms and this insurance often means you get matching item cover and so-on without having to add it on. If having such an expensive bike means the policy price is pushed up, the increase will likely be less than separate cover.
I just use the comparison sites and sift through to find the 5* policies, i think spend a short time sifting through them to find the ones with favourable terms for bikes suiting my needs (as a family we have about 7 bikes with the most valuable approaching £2k with accessories). Many need you to itemise bikes over £500 or £1000, for the sake of argument i usually list the kids frog bikes too.
I then usually email them with a benign question about needing to secure them to a ground anchor or whatever - essentially to ensure the cover meets my needs and to get a reply in black and white. I usually ramp down the voluntary excess to a level it starts to really bonk the price up.
As a measure I am currently Paying about £140 for Building and Contents i(and bikes) and I think i got about £30 cashback on topgashback too.