Unlike Seraphim and Cherubim, whose names come from vivid Old Testament visions in Isaiah, Genesis, Exodus and Ezekiel, Thrones rests on a much thinner scriptural basis: a single verse in Paul's Letter to the Colossians, which states that in Christ all things were created, whether thrones or dominions or rulers or powers, a bare list of four terms with no description of what any of them actually look like or do. Pseudo-Dionysius took that list, together with a similar one in Ephesians, as scriptural warrant for naming several of his lower and middle choirs, Thrones, Dominions and Principalities among them, effectively building visual and functional content that Paul's own text never supplies.
A separate throne-vision does exist in the Hebrew Bible, in Daniel's account of the Ancient of Days, where thrones were set up before the divine court convenes for judgment, but Daniel's thrones are seats rather than angelic beings, and Pseudo-Dionysius's choir of Thrones is not clearly drawn from that passage at all. The choir's whole identity, in other words, rests less on any angel actually called a throne appearing in scripture and more on Paul's bare word being taken up centuries later and given a place, an exalted, supermundane tendency towards higher things, within a hierarchy scripture itself never describes.