No, home depot does not sell them... Looks like you need to do a little research. You can find them in the SnS and power seller section here, from sumoregulator.com, greenleafaquariums.com, customco2, etc.
You need a regulator and needle valve, at minimum. A solenoid is helpful to be able to turn it off at night on a timer. Then you need a reactor or diffuser.