Scibor makes one dwarf gladiator, Signum Games has a Troll one, and years ago Games Workshop did a range of them for Mordheim, which included a dwarf and an ogre as well as various humans.
You can also convert them from ordinary fantasy miniatures with suitable heads and weapons - the usual suspects like Maxmini, Kromlech, Anvil Industries, Puppetswar, etc have such parts.