From LAS I would be searching extensively for AS-operated flights, too. The flex date calendar won't show them on the color-coded display but searches by schedule for a specific date will display them if available at Low band levels.

ExpertFlyer shows AS award inventory.

Alternately, look for supersaver awards on www.alaskaair.com - but AS may suggest some stopover routings that won't be legal under DL award rules. Then return to delta.com, search by schedule, and pick those AS flights.