We have an application that stores Trello card IDs in Airtable and I was having a hard time creating an automation in Zapier because there's no native way of getting the card by its ID (only to search by card name, which is not useful in our particular case as card names might change).
Since I couldn't find a solution in other posts, I decided to share how we did it.
You can get a card by its ID using an “Update Card” action (instead of “Find Card”). On the Card field pass the ID and leave all the other fields blank (so no fields are actually “updated”). This allows you to use the card from this step in further steps of the Zap.
Hope it helps.