Based on Boxflyers advice which is a US site, there is this in the UK:
https://www.ebay.co.uk/itm/BMW-GRANIT-GREY-MET-MATT-PAINT-CODE-963-TOUCH-UP-MOTORCYCLE-BIKE/291950949711
I cannot say if it is the correct paint. Can a motarrad dealer not advise?
That's where I got mine from. The same colour as the alloy wheels, as it turns out. I dropped the bike in the drive putting it onto the centre stand. Double value, as I also buggered the rear rim trying to get a tyre off.