That toyodiy.com. site is a great reference!
So here's what I found out:
The master cylinder part no. for Australian Delivered RHD cars is 31410-17070 (which matches what Toyota Australia told me so I have confidence in it). Here's a picture:

For US delivered LHD the number is 31410-17080. The picture is

. Spot the difference? No, neither could I.
For reference this is what the CBHaus eBay site is offering:
http://www.ebay.com.au/itm/270909905112?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 Once again it looks identical.
The system agrees that the slave (release) cylinder is identical across both LHD and RHD cars - part 31470-17030.
I have asked Lithia Toyota if they have either or both of these and will use them if I can. I've asked CBHaus if they have a slave cylinder. If Lithia can't supply for $150 or so I am going to risk it and order from CBHaus, unless anyone cares to warn me off for some reason. I'll post how I get on.