Hmm even if I have the sheath, I won't be able to make the weapon because of the missing ingredient.
That event that had the water gun ingredients was I guess the time I started playing Mononofu. Sad to say that I can only make Hibiscus during that time and was not to able to get the other ingredient for water gun and that summer headgear. That water gun is I think the best weapon if we are talking about speed boosts.
So I guess its copper burning time just to make the said equipments up to its current max level (Blacksmith is currently level 40 XD). Its better than nothing.