So, I've been looking around in the lava zone for a while trying to find infernape, I have already finished the game and he's the only one left for one of the attractions that I still need. I have ran all the way through the lava zone 4 times now and I still can't find him.
>Around the perimeter of the crater just outside Blaziken's lair. (Defeat Chimchar to make him appear)
According to Bulbapedia, Infernape is found in the Lava Zone outside Blaziken's digs. You have to beat Chimchar first. Chimchar is near the drill. I hope this answers your question!