A very significant percentage of Khergit horsemen and horse archers also spawn with maces, and their basic recruits often carry clubs. A few Rhodock crossbowmen spawn with spike-tipped wooden clubs for melee weapons. Since I tend to run about 50% Khergit mounted troops, I end up with a few prisoners after practically every battle, and usually add a few more on my own (a mace is my preferred melee weapon). The very best units to capture prisoners are your Companions, because you can equip them with suitable weapons for the task when it's needed, and otherwise when it's not. I also tend to pick up a few Slavers here and there by freeing captives of Sea Raiders and other bandits, and often actively pursue those parties with the "right" prisoners.
The main limitation of blunt weapons is generally distance, as most one-handed maces are only 70 units in length, while one-handed swords generally run 94-102 in length.