Xah'Rith the Keywarden in Act III - Stonefort (Infernal Machine of Terror).Sokahr the Keywarden in Act II - Dahlgur Oasis (Infernal Machine of Putridness).Odeg the Keywarden in Act I - Fields of Misery (Infernal Machine of Regret).
At level 70, each drops only one type (name of the Keywarden shows which machine they drop, and which material can be gained in result): At level 60, each of them has a chance to drop a single Infernal Machine.
The Machines drop from Keywardens on any Torment difficulty. Machines and materials chart by SparxxUI rates accurate for 2.4.1