There should be an small chance to find oil wells hidden underground, which you can further process into Plastic & Rubber.
As I've said in your generators post, this is probably going to be in the game too but it's good to see people who actually want this kind of stuff too XP
If it's not included into the game, there might be someone that's willing to actually mod the game to do so. I can't wait to see what the community will do with the mod-ablity for this game.
Just because it is short, doesn't mean it isn't good. But I do agree. On topic: What would you use plastics for?