The full title of HB 436 is: SA/SNZ HB 436:2013 Risk management guidelines—Companion to AS/NZS ISO 31000:2009.
This 144-page handbook includes every word of ISO 31000:2009, so there is no need to buy both. It’s available from SAI Global in print and download versions. I paid $A195.28 for my personal-use e-copy.
I recommend HB 436 highly. Many of the better points in this blog have already been made there, with genuine authority.