Only one I can think of is Korean from JFK-Anchorage, and yes you can buy tickets on this route.
You bring up a good point. This flight is code-shared, and has a DL flight number also. In that case, I guess it can be treated as a DL flight, and you can buy a DL ticket on it. I doubt, though, that you can by a KE ticket from JFK-ANC.
In any event, that flight does not show up on the Delta reservation system, unless you enter JFK-ICN.
"In God we trust, everyone else bring data"