It's been a while since I looked into the question, but I believe that the real thing (as opposed to those containing innocuous quantities of wormwood) can only be found in Eastern Europe.
There was an expert - I seem to remember that it was our Norwegian friend - 'Crasi' Dani and his Pits - who was a special friend of the Green Fairy.
Personally, I don't really like the taste - or the effects. If I really want to mess with my (remaining) neurons, give me a good old fashioned blunt, E. or some blow anytime.
Ah, the Simple Life....
Old Skool Rules.