Haven't got a clue mate. I think Smartdrugs are legal here, and so is weed. So you should be able to find that, at least, in coffeeshops.
I can tell you there's no street selling ****. I've been to amsterdam many times, never encountered anything like that. Edit: Not a tourist, though
Never bought drugs in Amsterdam or Anywhere, though. I've only been in a coffeeshop once, I really can't give you any advice on that.