Not to bump this, but you guys kinda stopped in the middle of Season 5. I think I can make suggestions.
I don't have a big list (yet), but I've thought of "The Lost Musket of Oliver Cromwell". I'll write it soon.
Scratch that, I'm not sure I want a weapon as an artifact on a kiddie show. Let's make it the Horse-Trampled Hat.
I think a weapon will be okay as long as the business end is dulled or broken off. Try reading my legends The Spear of the Nine Samurai or The Jeweled Sword of Charlemagne.
How about:
The Marble Block from the Lugouqiao
The Mystical Cutlass of Eustace the Monk (like I said, make sure to break off the blade in the legend)