Go to: Common market
Go to: Contracts
Go to: Offer contracts...
Scroll down: Enter 100%, mark the circle offer only local market contracts, confirm
Click on: Accept contracts for products your corporations need
At this point they are all marked 'skip', so scroll to the corporations that you want to contract to. Click in the second circle to mark local market
Scroll down to the first confirm that you come to and click it.
This should do what you want.
If anyone that may be reading this has a better way, please let me know. I'd like to know myself.