There is a website that sells a kit of all the grits and the leather and polishing compound.
Here is what it says: Our complete accessories kit includes everything you need to be a master knife sharpener. If you already have a 1 x 30 belt sander this will give you everything you need to sharpen like the pros. Kit includes 120, 320, 400, 600, 800, 1,000 grit belts, leather stropping belt, stropping compound, diamond serration file and safety glasses.
I could go without the serration file and safety glasses. You can also buy stuff individually.