LSJ
also κεν, Ep., Lesb., Cypr. (Inscr.Cypr. 135.10 H., al.), Thess. (IG 9(2).517.13, al. (Larissa)); always enclitic, = ἄν and κα; οὐκ ἄν… ἀλλά κεν Il. 13.290; οὐκ ἄν… οὐδέ κε 19.272, al. ; both coupled, ἄν κεν 11.187, Od. 5.361, Parm. 8.19, etc. ; [ὄσσα] κε θέλῃ Sappho Supp. 1.3; τί κεν ποείην ; Ead. Oxy. 1787 Fr. 1 + 2.16; κεν ἄν dub. in IGRom. 4.1302.51 (Cyme); εἴ κ’ ἄν (more prob. εἰκ ἄν) IG 5(2).6 (Tegea, iv BC); κε repeated, Od. 4.733.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)