We bought one a few months before our son was born. It says "TESLA" on the front, "zero emissions" on the top part of the back, and "...almost" lower down on the back. Here is a photo when our son was a week old in early 2015 (don't worry- we have a proper car seat for when the car is moving- and we now have a proper 40 amp 240 V charger at home)
We bought the same onesie in a larger size (18 months) in late February of this year at the Tesla store in Corte Madera, California. So they had them in stock at some of the stores fairly recently. Of course at this point he's kind of outgrown onesies so I don't have any pictures of him in the larger one.