Raptor Try the link below:
http://www.goldstarstockists.com/therest/revell-airbrush.htm
It's for a UK retailer, but I figure that shouldn't be an issue.
From what I know the Revell ABs are Thayer & Chandler Vegas, so all in all a pretty solid bet. Spares for the Vega brushes can be sourced from Shesto in the UK, see link below:
http://www.shesto.co.uk/
They don't list the spares on their web site, but if you give them a call or an email they will find what you need.
Best of luck.
Karl