I think I've worked it out. The searches are geo-restricted. My first few searches didn't include our product. It did say somewhere in the email that it was US only, so I searched whilst tunnelling through a US VPN node and the product was included, but I had used different search terms to when I was using an AU node and thought that that may have been the reason. I took the VPN out of the equation completely and searched using a vanilla connection. The results still included the product, so I posted the link above. However, I've just cleared my browser cookies and the link no longer includes the product in the results, so it's Amazon censoring results based on location.
