How do I post a 27" iMac with insurance?

As the title - I'm looking to sell my 27" 5k 2017 iMac in the original box, but can't find a courier that will insure it.

Anyone know of a courier that will insure an iMac? Obviously Apple are able to delivery them to customers, so there must be a courier that will? Not sure who Apple uses, but I've checked most of them.

Cheers for any help.