A couple quick ideas:
A group of goblins or hobgoblins, with an ogre in tow, have been spotted near Oakhurst. They have answered a call for reinforcements by the Goblin Chief Durnn. They are late and do not know that the chief is already dead. The two PCs need to get them out of the area, either by killing them or convincing them that they are too late.
Calcyrx's older sibling, a young (or juvenile) white dragon, has come seeking the lost white dragon. If the PCs have allied with the kobolds, the PCs must help defend them from the dragon’s attempts at rescue or rage (if Calcyrx is dead). Otherwise, the dragon vents its rage on Oakhurst.
A pod of twigblight has been seen on a local farm. The PCs are called into exterminate them, but during the battle, an ankheg is disturbed and erupts from the ground, striking at both PC and twig blight.
