You should call the manufacturer Chapin for these parts that you need. They are great helping our customers get the parts they need. You can reach their cusotmer service department at 1-800-944-4329.
According to Chapin you can use lacquer thinner in the Chapin Xtreme 3.5 Gallon Concrete Sprayer (#19049).
The Chapin Xtreme 3.5 Gallon Concrete Sprayer (#19049) has a GPM rate of 0.5-1.0 depending on the nozzle adjustment.
Yes Varsol and any other mineral spirits product can be used in the Chapin Xtreme 3.5 Gallon Concrete Sprayer. The manufacturer suggests rinsing the tank with water and pumping the water through the wand after use to clean it.