Amer Picon is a bitter, orange-flavored aperitif made from oranges, quinine, cinchona and gentian. It was invented by Gaëtan Picon (a Frenchman) in 1837. Back then it was used as an aperitif and as a treatment for stomach and digestion problems. It used to be produced at 78 proof, but the manufacturer has lowered the proof considerably since then. This has affected how Amer Picon mixes in drink recipes, unfortunately.
Finding Amer Picon can be tough. It is unavailable in the United States and even if you go to France to get it you still have to deal with the newer reformulated version. Fear not, your able bartender has tracked down two other directions you can go...
Your first choice is called Torani Amer. This is a liqueur made in San Francisco by the Torani syrup company. It is designed to fill in for the missing Amer Picon in the U.S. The best part is that Torani Amer is made at the full 78 proof like the original Amer Picon.
If you can't find Torani (it is not widely available) track down some Amaro CioCiaro. This amaro is similar to Amer Picon but not as fruity. Add a dash of Regan's orange bitters when using CioCiaro and you can approximate Amer Picon.