Magic of Faerun has a Wild Shape Amulet for 40k that boosts your level by 4 for the purposes of determining the types, sizes, and hit dice of creatures you can transform into.
The Skin of Kaletor, from Dragon 324, does the same thing for only 12k, but at a price. You take a -6 to all charisma based skill checks and wild empathy. Not a bade trade.