I've had some powder coated with very mixed results.  Due to them being pot metal, if they get too hot the metal will deform causing the lock to malfunction.  If the powder coating people keep the heat low and as short a time as possible, it works.  Don't try the newer slider handle, though.  It has a plastic insert on the inside of the lever that will melt.  I've never been able to remove that piece without breaking it.  I've had pretty good luck painting with semi-flat black then 3 coats of clearcoat, lightly sanded to reduce the gloss.
Steve Sandlin
Steve's Lock Shoppe