I bought my first kayfun(3.1 I think) from the classys here, it was a clone(no idea from what company) and it surprised me to how nice of a unit and once I got the wicking down it performed great. I then began to scoop up kayfun clones then decided to buy a original but not for the 150 bucks, I got a used authentic Russian91 from here again and it works the same as the clones. I must have a dozen kayfuns now sitting in a box in the closet. I went into fasttech and bought unsulator kits, bellcaps, plastic tank pieces, bases and a few useless quartz kits so I have plenty of parts.
I have no idea on where to get one now, I'm not looking to purchase one any more. Only place I can say is the classifieds they come through once in a while.
IMO if your looking to spend the bucks, spend them on a subtank mini with the RBA. The subtank was the reason I shelved all my kayfuns, easy to build on and vapes great.