Viper School Gear

Viper School Gear is set from base game The Witcher 3: Wild Hunt and from its first expansion Hearts of Stone based on school for witchers called School of Viper (from which came Letho of Guleta for example).

The Witcher 3: Wild Hunt
In the basic game set is in fact only two low leveled sword (one silver,one steel) previously owned by Kolgrim from Viper School, when you collect first of swords, it will start a new Scavenger Hunt sidequest.
 * Viper silver sword
 * Viper steel sword

Hearts of Stone Expansion
If you buy a expansion Hearts of Stone you can find remaining parts of Viper Gear.