Captain Miro appeared in a flashback during episode 12 "Mekaneck's Lament" on season 1.
Sadly he doesn't get much screen-time and is only shown on couple shots mostly from waist-up.
We see he has a Sword on his belt-holster, but he doesn't get to use it... or for the matter; show it in full view.
But here you can take a look at how Captain Miro's Sword looks like. A cool design and I for one would have loved seeing it get some use in the episode.
If we ever get Miro as a toy figure in the Masters of the Universe Classics line, it would be fantastic to see the Sword come as an accessory.