Easiest solution:
If you're a typical Fallout player, you've probably collected every kind of chem you've come across, so hopefully you should have tons of chems to spare for this.
Simply craft the two special chems Bufftats and Psycho Jet over and over again. Bufftats requires just Buffout and Mentats, Psycho Jet requires just Psycho and Jet. I had just about 50 of each chem so it was no problem for me. Takes about a minute or two to get the achievement doing this method depending on how long it takes for you to spam the A button.
If you need to find some chems there are plenty of traders across the game world that sell them. Obvious ones being the one in Diamond City in the market area, Wolfgang at Drumlin Diner if you sided with him, Doc Weathers who wanders the Commonwealth with caravans (can sometimes be found in Bunker Hill). And of course, chems are located ALL over the world in containers. You should be collecting chems already to have enough to do this method.