They sell Zoysia seed at Lowes. I bought mine there, and I can tell you that if your yard is shady, don't plant zoysia seed. Half of my yard is shady and the other half is in total sun. The sunny half is completely grown. It looked like a mature yard in less than a year. The shady side is VERY spotty.
I HIGHLY recommend zoysia seed in a shade-free yard though. Grows very slowly and hardly ever needs watering (once grown, of course).