On tap is a common phrase that refers to something that is readily available and easily accessed. The antonyms for the phrase are 'scarce,' 'limited,' and 'unavailable.' Something that is scarce is difficult to find, and it's not easily accessible. Limited refers to something that is available in limited quantities, for a short period or available to a specific group of people. Conversely, the term unavailable means something is inaccessible and not immediately accessible. The phrases' antonyms can create diverse meanings depending on the context of usage. However, they all connote the unavailability or limited access of a particular thing, substance, or service.