Help with a Panasonic KX-NCP500

Can I ask ..

I have a Panasonic KX-NCP500. It has a 16 slot card for 16 x KX-DT333 system phones and 16 standard line telephones. Does anyone know the latest system phone handsets that will be compatible with the KX-NCP500 ideally with 24 programmable keys or more ?

With thanks in anticipation