It definitely isn't rare, and it definitely isn't found only in poetry. Any good Latin grammar will address this topic.
In Gildersleeve and Lodge, Latin grammar, the index entry for esse includes a subentry for 'omitted.' The main section where this topic is treated is 209. It gives a general rule, examples, and then notes, including a note that addresses ...
Here's a partial answer. Common in proverbs, and possibly epitaphs, which are not exactly poetry.
'Ars longa, Vita brevis,' The life so short, the craft so long to learn (Chaucer)
'Ad augusta per angusta,' Á des résultats augustes par des voies étroites. (quoted in Hernani: Victor Hugo)
'Amicus Plato, sed magis amica veritas,' ...