Was looking over the monsters in the Mordenkainen's Tome of Foes book for those and can't find them anywhere.

These?

https://www.dndbeyond.com/compendium/rules/mtof/bestiary#AirElementalMyrmidon

https://www.dndbeyond.com/compendium/rules/mtof/bestiary#EarthElementalMyrmidon

https://www.dndbeyond.com/compendium/rules/mtof/bestiary#FireElementalMyrmidon

https://www.dndbeyond.com/compendium/rules/mtof/bestiary#WaterElementalMyrmidon

Ya was surprised not able to see those not in Mordenkainen's tome. By the way, those I can't see. But I found them in the that Prince book, I think. Maybe thats where they come from first before Mordenkainen's tome.

They were originally released in princes of the apocalypse, but were later release in mordenkainen's tome of foes. They are in chapter 6 of MToF.

Thanks for the info.