The screws that go into the side of the mixer are the same ones that hold the side cheeks on. Remove the side cheeks and use the same screws to put rack ears on.
The screws that go into your rack to hold the mixer into the rack do not come with the mixer. These are 10/32" size. You can buy these at any hardware store or through a commercial radio parts supplier Mid-Atlantic Products, Pacific Radio, Tec-Nec, Sweetwater, etc.