Where can I buy a second hand sea kayak?

Hi there,

I am looking to buy a second hand sea kayak for 2 people.  I am not really too sure where to look...

Does anybody have one to sell?  or know of a good place or website to go searching?

And if I cannot find one to buy, do you know where I could rent one? Either on a daily or weekly basis.  I am based near Sai Kung.

Thanks for all your help,

Jules