Well if it's role play why do you need to actually find the drug?
This is very serious, I can tell you right now any drug that induces unconsciousness is potentially fatal. That is why anesthetists are needed and paid so much, its a tricky balance of knowing the effect of the drug vs weight and other physical and physiological indicators. Get that wrong and someone could react badly, go into a coma or stop breathing. Yes you see it done in movies all the time, in real life people get it wrong all the time.
Be careful, this isn't something to fuck around with.