Amazon has Vol III in stock but hasn;t gotten Vol IV up yet. Baerns & Noble and BooksAMillion both have order entries for Volume IV.
Amazon should be soon, but will prbably sell out right away. Barnes & Noble is sold out, but their new order was just printed and is on the way as we speak.
I just got my Vol IV yesterday from BooksAMillion. Looking forward to some great holiday reading. I really enjoyed the first three.