I can find no reference to stats for weapons or armor made from ivory in 3.5. (Note: BESW found some)
Athas.org, in the Dark Sun Campaign Setting, describes the inferior materials used on Athas, due to the scarcity of metal, as including bone. Since ivory is just bone, this could be used for ivory. Normally-metal weapons made from inferior materials apply a −1 penalty to both attack and damage rolls. Note that Athas.org, though they received official permission to produce Dark Sun material for 3.5 from Wizards of the Coast, is still a third party publisher.
This is irrelevant, however, as
Druids can use metal weapons
Druids are prohibited from wearing metal armor.
Druids are proficient with light and medium armor but are prohibited from wearing metal armor.
(Player’s Handbook pg. 34, emphasis mine)
Not from any other metal items. They can use metal weapons, or metal whatever, as long as it isn’t armor.
Consider:
Weapon and Armor Proficiency
Druids are proficient with the following weapons: club, dagger, quarterstaff, scimitar, sickle, shortspear, sling, and spear.
(Player’s Handbook pg. 34, emphasis mine)
A dagger could be made from stone, but it would be quite inferior to a steel dagger, which is the weapon we have stats for. A stone (or ivory) scimitar or sickle just isn’t going to work, and generally the spearheads in play are also steel. So literally ⅝ of the druid’s weapon proficiencies are in weapons that are made from steel.
Why they cannot use metal armor, but any other metal is A-OK, is anyone’s guess, but considering that the example druid in Player’s Handbook is statted with a scimitar, which she clearly has in her hand and is clearly made of metal in the accompanying illustration, this does appear to be entirely intentional.
