"Now what black satin paint to use on roll bar? Any ideas?"
You could look at John Deere Blitz Black with hardener. If you don't like that there are some semi-gloss, black hot rod paints available in urethane. Look at the TPC Global website in the left menu column are "Hot Rod Flatz" paints.
Or, you could go to the Easwood Automotive website and look at the various chassis blacks. I use the 2K Ceramic Chassis Black. It is a 2K urethane that comes in satin or glossy. It has a ceramic additive to it and is fairly chip and scratch resistant.
You just need to really mix/shake the paint to incorporate the ceramic into the paint carrier prior to spraying and you need about a 1.7 tip to make it work without thinning excessively.