Home Postcodes by state WA 6420 Postcode 6420 6420 is the postcode for 2 localities in WA: Cramphorne and Muntadgin. Localities with postcode 6420CramphorneWAMuntadginWA Postcode 6420 State or territory Western Australia (WA) Localities 2 Council area Narembeen; Merredin Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6419 · Postcode 6421