In Baldur's Gate, if you met Coran and accepted his subquest, you can hunt down one wyvern and sell its head for 2000 to the governor of Beregost. Other heads can be sold to Officer Vai or at stores that will buy this item (e.g. Thalantyr at High Hedge).
In Baldur's Gate II it can be sold to stores, but there is nobody who collects wyvern heads or uses it to make something. Wyverns which are summoned by the 6th level wizard spell Wyvern Call will drop this item if they are slain.
It weighs 30 pounds.
|“||The severed head of a wyvern is both a fearsome and a reassuring sight. Gruesome as its fanged maw and blazing eyes may be, there is consolation in the knowledge that they can be conquered by mere and lowly mortals.||”|