I would use a PTO pump for a sprayer. They are 6 or 7 roller pumps. Any farm store will have them, TSC for one. You might want to put a large strainer on the inlet end to keep the crap out of your water and pump.
My limited exposure to PTO pumps, is that they're usually designed for high volume flows and are expensive. In your instance, a small gasoline pump like those found at Northern Tool, may be more economical and convenient too.
I made my own from a pto pump off and old 1 ton county fire engine. Made it fitan old carry all I had and turned down an adapter shaft allfor about 50 dollars and some labor.