When Reinhardt and Dr. Liebermann search the brothel again, Liebermann finds a quadruple Sharps .22 derringer. Production of this weapon ceased in 1874 and these weapons were not sold in Europe. So it is impossible for Liebermann to find one in an Austrian brothel.
The previous person stated, " Liebermann finds a quadruple Sharps .22 derringer. Production of this weapon ceased in 1874 and these weapons were not sold in Europe. So it is impossible for Liebermann to find one in an Austrian brothel." He speaks in absolute terms by saying it is "impossible".
Maybe UNLIKELY, but certainly not "Impossible". While the Derringer cited was made in Pennsylvania, transatlantic travel was becoming more and more popular after the end of the US Civil War. Many people brought fire arms on ships. It is very likely that at some point an American traveler or businessman carried a weapon such as this over to Europe and it could very well have ended up in an Austrian brothel.