The pilot reported that the flaps became asymmetric when full flap was selected at about 300 ft on final for landing at Palm Island. The pilot immediately returned the flap selector to the previous position and carried out a "go around". The flight returned for an uneventful landing at Townsville. Post flight examination found the right flap extend cable had failed in the radius of a pulley. The cable was due for special inspection in approximately 20 hours flight time. The maintenance organisation, Operator and CASA Airworthiness in Townsville were all contacted concerning this incident. The maintenance organisation is currently submitting a Major Defect Report detailing the failure. The maintenance organisation will be recommending to CASA that the affected cables be placed on a shorter special inspection period, or be replaced at short time intervals.