In other lexica (Hesychius sigma230, Photius sigma88 Theodoridis) this lemma is *sarphdw\n a)kth/, regarded as a fragment of Sophocles (fr. 46 Radt); however, the Suda's one also appears as proverbial in Zenobius 5.86.
Two promontories of this name are known (neither of them obviously connected with the Homeric hero Sarpedon: sigma 146): one in Cilicia (Barrington Atlas map 66 grid D4) and the other on the coast of eastern Thrace south of Ainos (map 51 grid G3). Presumably the second of these is the one meant here; note in any case Steph.Byz. s.v. 'Sarpedon, a city of Thrace'.
[1] Adler cites Crates fr. 54 Kock, while noting that this is more probably Crates of Mallus, the Hellenistic grammarian (kappa 2342); this is accepted by Kassel-Austin, who do not include the fragment. See rather Crates of Mallus fr. 13 p.72 Wachsmuch = fr. 127 Broggiato.
[2] For Okeanos see omega 43; for Gorgons, gamma 390.