You can get a cake of this at the same place. It's better, if possible, to clamp the drill or somehow fasten it securely and hold the trombone against the wheel, rather than trying to hold the drill and control it. After you've polished the trombone, it has to be absolutely clean and bone dry before you spray it or the lacquer won't stick. If you clean it with water and detergent, it will tarnish the brass. There are other solvents that are better, like acetone, but they're flammable and bad to breathe, and they might dissolve the remaining lacquer.
Alcohol works OK and it's safe.
Wipe with dry cloth or paper towels, then spray in a safe area. Lacquer is flammable and you need some ventilation, but you don't want any fan motors running where you're spraying. It's best just to open some windows. A garage is a good place to spray, or a tool shed. The water in the lacquer may not all escape before the lacquer dries, and then it won't stay on.