"The Toroid orbs drop from enemies in specific locations on Orb Vallis (Vega from Spaceport, Calda from Enrichment Labs, Sola from Temple of Profit). Can rarely drop from enemies in caves."
https://www.reddit.com/r/Warframe/comments/9vj92d/so_how_do_you_get_toroids/
https://www.reddit.com/r/Warframe/comments/9vj92d/so_how_do_you_get_toroids/