Plants/Fishing/Stones

Sola Toroid	Temple of Profit	Drops from enemies around/inside the Temple of Profit. Has a 20% chance to drop from Kyta Raknoids. Go inside the target area. Try to get one of the enemies to put down a Reinforcement Beacon. Wait until the beacon hits Alert Level 4. From this point, unlimited enemies will spawn. They will increase in level very quickly, but will eventually hit a level cap that is based on the bounty tier, and stop increasing further.
Vega Toroid	Spaceport	Drops from enemies around/inside the Spaceport. Has a 1% chance to drop from Mite Raknoids. A large number of Mite Raknoids will spawn during the first stage of Exploiter Orb whenever she moves across the battlefield
Calda Toroid	Enrichment Labs	Drops from enemies around/inside the Enrichment Labs. Has a 20% chance to drop from Scyto Raknoid. Doing all of a Profit Taker Phase 2 bounty but not turning it in will endlessly spawn Corpus dropships. You don't even need to let the beacons hit Alert Level 4 since the drop ships will bring plenty of enemies.
Crisma Toroid	Profit-Taker Orb	Drops from the Profit-Taker Orb upon defeat during Phase 4 Heist.
Lazulite Toroid	Exploiter Orb	Drops from the Exploiter Orb upon defeat.