Where do you get the tokens needed to build the pumpkin soup pot?

You can get a fixed amount of the candy each day from the 'Login Reward' benefit, you just need to go collect it from the benefits menu.

Also during the Halloween Treasure event, when you attack the zombies as normal in the world map you can earn Broomsticks (up to 100 per day). These can be used in the items menu for rewards or exchanged to Wizard hats which when used will give slightly better rewards.

One of the rewards you can gain are 'Candy' items that are then used to unlock the pumpkin soup pot.