Wirt’s Bell is the easiest to get provided you have the 100,000 gold to purchase it. The NPC Squirt the Peddler can be found in the Caldeum Bazaar in Act 2. Along with the bell you will also recieve the achievement Wirt’s Case Scenario as a bonus.
The Gibbering Gemstone drops off a random spawn named Chiltara in the Caverns of Frost Level 2 in The Fields of Slaughter in Act 3. This is the same area which you kill the ballistae and trebuchet for the quest Machines of War. If you take the Bridge of Korsikk waypoint and head northwest a bit, there is a spawn location for that cave closeby. Unfortunately, it also shares the spawn with the Icefall Caves, so it may take a few tries to find it. Chiltara will be a rare spawn and not always be up. Once slain, the gemstone will be yours.
Staff of Herding
To put all this together, you need the Plans: Staff of Herding. This will drop from Izual at The Great Span in Act 4. It will not always drop, so you may have to kill him a few times. Once you get the plans and teach them to the blacksmith, you can craft it using the materials you collected and 50,000 gold.