If anyone who is using the version that allows all 3 of the lizard parts to be gotten and want to find them for that gate, they are found in the follow places:
Head=Swamp (This is part of a story to unlock the Ruins)
Tail=Bandit Camp (This might be part of a story as well, it is picked up when Tank was chasing the bandit in there at night)
Torso=Lizard Egg Quest from the Witch in her hut during the day (This one you do not pick up as part of the story but after completing that quest, this one can be missed if you don't look for it.)