A few ways I know of getting a bunch of this include going to drops that are yellow or above and taking the stuff made at a fabricator and grind it or you can take an anky mine some obsidian rocks and take a megatherium to a cave with a bunch of bugs and than use a doedicurus to get a bunch of stone or you could kill a bunch of titanyroma drones and soldiers with a frog
I found out about the converter trick, but it requires you to be either a kairuku breeder or have an achatina or two. According to the tip givers, just craft some structures using the organic polymer then (for casual players only) demolish it. Should give you normal polymer. Reason is organic polymer only stacks into tens, while normal poly into 5000(on mobile). Useful for every midgame item.