SmartPlug sales have taken off dramatically and demand is high, and for good reason. That said the product is out there and is available.
I will be honest here and say that I MUCH PREFER a new cord set and inlet as compared to the "retrofit" kit shown to the right. If your old yellow cord is in good condition then replacing the boat end is a suitable option. If however your corset is older, do yourself a favor and buy a new cord set and inlet.
Where do you buy a SmartPlug?
The crew at Sailboatowners.com (LINK) are really great. They have good prices, great customer service, are in close proximity to the SmartPlug facilities which means they have great access to inventory.
Lots of places have the SmartPlug but for on-line purchases I really do like these guys. I have included some links to the various parts to make ordering easier if you choose to do so.
Purchase SmartPlug Retrofit Power Cord Plugs (LINK)
Purchase SmartPlug Shore Power Inlets (LINK)
Purchase SmartPlug Cord Sets (LINK)
EDIT: PLEASE be patient. This article and some others have generated a large demand and supplies may be limited. They are working to fill orders as fast as they can..