Checked out a local shop that stocks Hammerite and they only stock Black and Silver, so I may need to get them to order in, if they will that is.
The other alternative I have thought of is from my other hobby (building model cars) there are paints by Tamiya for replicating Airforce paint jobs, with many shades of gray available I should be able to replicate colour quite easily, if anyone wants to check them out, check the AS- line of paints