After clearing out the Jackal Canyon, as you leave cross the bridge and get in your car (or you can walk but it takes longer). Follow the road and as the road Y's go to the right of the Y (the map will tell you to go left and head back to subway town).

As you come down the road you will hit a door, turn your car around and to your left under the the rocks there is a comet bloom, and right next to that one is another one.

Go back into the canyon and come and and repeat all this. Once you have enough (I stopped at 30) go back to the shop and sell all of the flowers for 65 a piece.

Don't exit the shop, buy back all the flowers you just sold for 43 a piece ($22 profit per flower) and do this as many times as needed.