I dunno where it came from but I had a few different seeds at the beginning. I didn't see them before I made another stockpile and the guys grought them them there.
After that I just check what they was and made the fields.
I also found mushrooms far away in a "cave". It was rock with some dirt in it. Easy to spot them. Harvested the mushrooms and they started growing them.
There's still more ppl that join than you can ever feed in a proper manner. I sent someone off to gather some berries and they ended up dead because they didn't have food with them. Another one also died of dehydration just becuase he took a longer route getting back into the base :P