This guide will let you know where to get the Tempo Royale in Warframe.
Tempo Royale can drop as a reward for doing Rathuum on Sedna, on the Nodes Yam and Vodyanoi. The mod has a very low drop chance as a reward, so it will likely take you some runs before you get it. And if you don’t want to farm that, you can always buy the mod from someone through trading.
It is recommended to bring tanky or frames that can do a lot of damage, chroma, rhino, nidus, etc.
It’s probably going to take you some time before you get it unless you are lucky.