Ok guys, here it is, Version 1 of my particles as matrices script.
First let me say that there is a bit of a bug in it. There is something not 100% in my math which generates the matrix. The result is that the object is becoming skewed. If anyone would like to take a look at the script and if they can spot the error then please let me know or fix it and repost.
Ok, here is what you need to do. The script can be installed as an add-on in the same way as any other blender add-on. It will appear in the "import-export" section of the add-ons list. There is another bug here in that I am unable to tick to include the "Export particles as matrixes" (excuse the typo, I will fix it sometime) add-on. So I think that every time that you run blender you will have to go into the add-ons and tick the add-on. This doesn't actually tick it but it does appear to activate it. Again if someone can fix this then that would be great.
Once you have it installed then create an object and add a particle system to it. set the system up how you want and when you are happy with it press space and type in "export matrices" and select it from the menu. Once it is running you will see an export window appear where you can tell the script what name to give the export file. When you are happy press the "export Matrices" button and all of you particle data will be output to the file in matrix format. All you then need to do is open the file and copy the contents into the scatter node in Octane. Bingo, lovely instances.
As I say, version 1. Please play with it. Please report any bugs. Please fix the bugs if you are up to it because I am not a python programmer. Just this script has taken me about 7 hours to cobble together from various places. There is that bug in the math which is causing the object to skew but I am tired and I've had enough of this thing for tonight. At least it is almost there.
Happy scattering
Steve