I know this is a long wait for a response, But I just saw that it wasn't answered and I have found a paint color. In the U.S. VHT Brand with Part Number SP189 Color Graphite is very close and seems to be a good quality Polyurethane. .
I find VHT generally speaking a very good paint. Their wheel paint in silver is the closest "off the shelf" match I found for the fan and radiator grill. Closer than a couple of other brands I tried and then compared to an NOS one. Not an exhaustive test by any means but a pretty close match.
I also like their Roll Bar and Chassis paint in satin black for radiators, calipers and master cylinders. Once again, not perfect but not bad at all and very durable.
I had a particularly fastidious friend tell me just the other day that VHT bumper paint in black (I think he said in Satin) was perfect for repainting things like plastic chain cases or the black plastic of the front half of rear mudguards that some bikes have.
Sydney, Australia. The new leaner, trimmer shed: RE5M, RE5A, GSX1100EX, GL1800/Champion sidecar
He had a clean sweep of every award available when he showed his first ever restoration at a national rally (KZ1300).
Now he's working on an RG500 and the level of detail he's gone to is staggering. Right into the metallurgy in his attempt to exactly replicate the original finish on the frame. And he's got some bloke who has a printing process directly onto metal to replicate the switchgear. The list goes on.
Rumour is he's also got a girlfriend, but I don't believe it.