The only way to buy the AV EVSE is through Aerovironment. Many people have done this (myself included) and had their own electrician do the install, saving a lot of money.
I would suggest you look at all your options listed on the forum as you can save quite a bit of money over cash and carry AV. There are also a few people selling their AV units every once in a while because they upgraded their Nissan EVSE and they no longer need them. There are better options IMO.