There are actually stones for weapons.
Here's a complete list of all tabs you can pick in order to make stones from them.
I've added the weapon tablets here.
Jade tablet of discipline - Weapon blocking
Jade tablet of Int - Increasing the int on your weapon
Jade tablet of master - Increasing the durability on your weapon
Jade tablet of Str - Increasing the str on your weapon
Jade tablet of strikes - Increasing the attack rating of your weapon
You can also add immortal stones,steady stones,astral stones and lucky stones. But they doesn't improve the stats on your weapon.