Actually, DL codeshares on KE's ICN-CTS flights. DL7905 (operated as KE765) flies ICN-CTS and DL7904 (operated as KE766) flies CTS-ICN.

Not sure why you wouldn't be able to book these on delta.com, but I assume you could do so over the phone if you wanted to do that routing. DL codeshares on KE's US-ICN flights as well if you want to keep it all on a DL ticket.