Sir or madame,
If you go to Home Depot, Lowe's or any other major home improvement store, they will cut plywood to size for you. You can call ahead and ask for the lumber department. Tell them what you would like and they will have it ready for you to pick up. Very easy, very quick. Trust me, I used to do home remodels. I saw people in there getting stuff cut on the big panel saws all the time.