All Materials can be acquired by simply playing the game! Squashing spider mites, leveling up, opening ganja chests, and completing quests all have the potential to reward Materials. Some Slackers will even give out Materials! You can also find specific materials to purchase on Floydslist or even your friend's dispensaries!
TIP: Once you've got your Bus Stop unlocked, keep an eye out for a scruffy-looking guy named Zeke. He'll trade buds and products for MATERIALS!