Peter McDowell is the only person selling Wizard green that I am aware of. You will find it at www.nymarine.ca. The kicker is shipping across the US-CAN border. Takes a bit and it is pricey. But, if you want a perfect match and a good quality paint, Peter's is the way to go. If you aren't concerned about perfection, you can try matching it to a Duplicolor paint, but I haven't seen a real good match out there.
Another option ... if you have a few flat spots of good quality original paint on the motor, you can also find an auto paint store in your area and have it mixed. They should be able to match the color from the original without too much trouble.