Hi and welcome!
There is no such thing as a "genuine" Vamo - actually, it's more accurate to say there's no such thing as a knock-off Vamo. KSD has been reported to be the company who first introduced the device, but even if that could be documented, they may not have been the first manufacturer. The Vamo has been around for awhile and at one point was known as the Bamboo (there's another mod out now called the Bamboo, which is completely different). See? Clear as mud.
There are many different manufacturers and not all Vamos are the same, even ones bearing the same version designations. It's kind of a toss up. You have over 5 posts, so you may want to visit the Vamo sub-forum in the APV section to see where people have bought theirs. FastTech often has the best prices, but some people prefer to buy in the US.
Vision (the company who brought us the Vivi Nova and the Spinner) have recently started to offer a Vamo and there's a pretty good price at Mad Vapes: http://.........blogspot.com/2013/12/its-eve-visions-gun-metal-vamo-2850-usa.html