Satin black spray paint is what is commonly used to refresh wiper arms.
Mask the arm off to prevent overspray, then wipe it down with alcohol and let dry.
Mist on the spray paint over the entire arm. Satin and matte spray paints are very forgiving compared to glossy regarding evenness of finish once it dries. You can mist on one coat and let it dry a few minutes until it's satin and see what you think. If it needs it, hit it again.
You might approach a reputable car detailer in your area to do this since it's a very common procedure for us in the industry.
If all of this sounds daunting then follow cypho's advice and buy a new wiper arm.