There are several ways to obtain goods. You can produce them yourself by constructing goods buildings according to your requirements, or you can trade with other players for the goods you need in the trader. Goods can also be purchased with Diamonds. Guest Race goods can only be produced by yourself and you can not trade those with other players.
Hint: You should only produce boosted goods in your own city. Boosts for goods are unlocked via research and increases to these boosts can be gained as a reward for collecting Relics, so you should keep an eye on those!