I've ordered one of these
https://www.ebay.co.uk/itm/Vortex-Flip-Cap-Optic-Cover-size-FC-3-4-5-6-7-/322847055701
Vortex-Flip-Cap-Optic-Cover-size 7.
It's suppose to fit 55-61mm. It cost £12 with free postage but it could take until the 9th April to arrive. I'll let you know if it's any good.
The lens cap has arrived. The Size 7 is a nice tight fit on the end cap and provides a wide band of rubber to protect the end of the scope. I feel it is a good addition to the scope.