I want to get a specific type of weapon for a hunter I have in game, but I haven't been able to find mention of one. Is there a sledgehammer of any kind in game?

as a weapon I don't think there's one that looks like a hammer but there are camos like Thor's Hammer that is a giant hammer

To add on to what @Jamesmor said, in this game, outside of a couple of Camos for Swords, you will find that most Hammer-like weapons are Wands (the Techter weapon).

Duly noted. I'll keep an eye out for such camos.