Reaper is a good source for most things odd...
You should be able to order the head sprue from this set on its own from their Bone Yard:
http://www.reapermini.com/OnlineStore/head/sku-down/03457
You can browse through their catalog and find other dragons/lizards often with separate tops of the head (to give a gaping maw). Reaper will sell the parts in most cases. If it isn't listed on the website on its own, fire off an email to them, and Kit will usually create a new entry for that items parts.