Thanks, I made a .nbt file that works with the below:
I have not tested it yet, but LordSmellyPants also suggested:
Entity(0,0,0,ElderGuardian,1) with no text file required.
His method is probably the cleaner solution for 1.12, but I have not tested it yet. For anyone that stumbles upon this later, if his method does not work, you may use mine.