Auto spray gun will do a better flatter job - that's all, dust control is better at a pro shop too.
Nino: Tried paintmobile? (They're in Dandenong)
They make a "Acrylic Clear" in a aerosol (I have 1) , they probably do it in a 1lt/4lt tin as well?
Also have a polyurethane clear listed on the website.
I thought the gun trick was to use 2 pack clear? (Which they probably sell)