Hi David,
Firstly, Happy New Year.
This is certainly not something that is new or unusual.
At the heart of the problem will be what is known as the "Wassenaar Arrangement on
Export Controls for Conventional Arms and Dual-Use Goods and Technologies".
This is a an agreement between 40 member nation states to try and prevent some items
falling into the hands of a list of some other countries. The "other countries"
read as a "Who's Who" of the usual suspects.
Anecdotally, these type of controls have existed throughout my own professional
engineering career and before that, dating back to the early days of the Cold War.
Over the years I have been required to routinely sign US Export Control
Restriction agreements and for example, this is quite common in the semiconductor
industry. There has been a renewed recent flurry of these in the past few months alone.
The McMaster Carr policy probably has its origins going back to 2003, when it
was fined by the US Department of Commerce for failing to report eight sales
to various Middle Eastern states.
See
http://www.bis.doc.gov/news/2003/mcmaster_carr.htm
It can be tough, as some specific hardware can be difficult to source in Australia.