Buffalo gourd seeds are possibly the most common consumables from plants in-game, being both sold by most food vendors and located in numerous areas. The plants themselves grow on cracked or broken roads and, due to their contrast of color against the roads, they are very easily spotted.
They are most often found scattered along the cracked roadways while traveling the Mojave Wasteland but they can also be found in several locations.
Mojave Outpost - Five plants are located in the picnic area behind the Headquarters building, and three across the road by the brahmin pen.
Lucky 38 - Seven can be found on a shelf behind the bar on the east side of the casino.
Goodsprings - Three seeds are found in Doc Mitchell's house at the beginning of the game. They have no ownership, and can be taken without the player losing Karma. There are several other plants located around Goodsprings.
Primm - Two plants are located right outside Deputy Beagle's Residence.
HELIOS One - Several can be found in the Power Plant building's last room next to the Observation Room door.
In the Big MT, there are terminal entries describing how one of the scientists choked to death on one, and was reanimated by his trauma harness. After a botched attempt to get rid of him, he acquired a cyberdog gun, and can be found and killed. However, his inventory does not contain any seeds.