Thank you to everyone who replied to my query about airbrushes below. I have got the message that an airbrush may not be up to the job for 5" gauge due to delivering enough paint to maintain a wet edge and also the viscosity of enamel paints.
I have a further question about air compressors which were mentioned in the replies. Although I have a small air compressor as I stated delivering up to 40 psi, I also have a larger Tiger Airmaster compressor from Machine Mart rated at 2.5 HP and delivering 9.5 CFM. Would this be adequate to drive a small HVLP spraygun? The compressor is actually a pretty beefy machine! If so I will purchase such a spray gun.