As requested by Espen204 here's an updated map with Oleander Sage locations if you guys/gals would like any other additions please feel free to send me a message. Happy trails y'all! :
Oleander Sage - Red Dead Redemption 2 Wiki Guide - IGN
Garden Sage: mites, scorpions, oleanders
Flora of America | 12 Collectible Cards Locations - Red Dead Redemption 2 - Playthrough Guides
Red Dead Redemption 2": Herbalist Challenges - LevelSkip