Here are the ways you can get more Zoo-tokens:

• Collect tokens from the Fountain (don't forget to increase its level to collect more)

• Complete Regular Tasks

• Catch butterflies in other players' zoos

• Fulfill requests for baby animals

• Get new levels and statuses

• Complete certain Quests

• Complete Tapjoy tasks

• Finally, you can purchase more Zoo-tokens by pressing the green "plus" button at the top of the screen