There are twelve crops here that vanilla does not have: cabbage, chinese cabbage, corn, eggplant, garlic, grape, hop, pepper, pineapple, pitaya, rice and tomato. Each one only exists where it exists on Earth.
They grow wild and fully grown in the places they come from. In the middle of a crop's range you will find patches of five to eleven plants. Near the edge of its range you will find small patches of two to four. A plant stays where it is until somebody breaks it. Villagers in the right latitudes trade them too.
A wandering trader will never sell you a crop you could plant. If you want a crop from somewhere else, you go there, or you find somebody who did.
Finding out what is near you
/croptrades here prints your latitude and longitude, the biome you are in, and every crop whose range covers the ground you are standing on. It also names the crops the biome turned down, and why, which is usually the more useful half.
/croptrades on its own lists which crops are traded where.
The first harvest
The first time anybody brings in each crop is recorded once, for that crop, for ever. Once a crop has been harvested, that entry is gone for good.
Farming these crops also pays mcMMO Herbalism experience.