If you're looking at getting Apple-branded caps, you're better off buying a whole new keyboard. Apple-branded caps sell for a hefty price.
All TiBook keyboards are slightly different. They use different connectors, and the "gigabit" TiBook first introduced two "Apple" keys. Key caps are interchangeable, but I wouldn't recommend buying caps from
www.pbparts.com if you're looking for a bargain. The Apple Store was very good about handing me a free, extra "fn" key when I took a Ti into the store.
Considering Apple TiBook keyboards start at $200, neither solution is preferable. Your only alternative is waiting for a KeyBorg series for the TiBook.
A recommendation for the future: external keyboards.