Wild Feverfew: can be found in many areas of New Austin, primarily in the area around Thieves Landing.
Desert Sage: can be found in the area around Gaptooth Ridge in New Austin.
Red Sage: can be found in the area around Rio Bravo in New Austin.
Prickly Pear: can be found in the area around Punta Orgullo in Nuevo Paraiso.
Wooly Blue Curl: can be found in the areas around Perdido and Chuparosa in Nuevo Paraiso.
Butterfly Weed: can be found in the area around Diez Coronas in Nuevo Paraiso.
Hummingbird Sage Flower: can be found in the southern area of Tall Trees in West Elizabeth.
Prairie Poppies: can be found in the eastern area of Beecher's Hope in West Elizabeth. Can also be found in large amounts by the train tracks at the bottom of beecher's Hope (most being between the word 'beechers hope' at maximum zoom out and the train tracks
Golden Currant Leaf: can be found in the western area of Great Plains in West Elizabeth. This is probably the easiest one you'll do if you stay on horseback to look for them as they stand out a mile away
Violet Snowdrop Leaf: can be found in the northern area of Tall Trees in West Elizabeth.