What would Gorum send?
An iron elemental, maybe (take an earth elemental and up the AC a bit, add spikes). Or a fire elemental made of molten metal (a bit slower but its touch is heat metal instead of burn). A CN salamander, perhaps?
Generally I'd say this is a GM call, but with Gorum I'd be looking at outsiders with fighter levels, or maybe barbarian levels. I think there's something in Gods and Magic about Gorum's usual planar allies, but not with stats, so you'd still have to make them up.
Whatever it is, make sure it's in armor and has spikes.
I'd look to the customized summon list in the Gorum article—there's no reason you couldn't call those creatures with planar ally instead of summoning them with summon monster. So: iron cobra (with no poison), bulette, behir, gorgon.
Obviously this is limited by the HD of the creature, but that should give you something to start with.
Likewise, rank-and-file armored celestial warriors/fighters/rangers would be appropriate.
Also, if your GM allows it, you could just call an "iron" version of a HD-appropriate monster. Increase its armor by +2, make it vulnerable to rust attacks like an iron golem, and you're all set. Iron harpy, iron ogre, and so on.
Or just pick a monster with DR or that's suitably resistant to physical punishment, "reskin" it as an iron creature, and roll. For example, a gargoyle doesn't have to look like stone, it could look like an iron statue and have the same stats as a normal gargoyle.
