Yes, it's time for the Iron Guard.
These stalwart defenders of humanity guard the Firstborn cities, and unlike most real life guard duty professionals are actually hypersuperultra elite soldiers.
This is another set of retro-clones, i.e. I tried to imitate the style I used for the first batch of these about ten years ago.
I'm running out of Firstborn as well, I'll do some Black Sisters and Desert Crusaders next month but then I have to think up something new for December.