Well, after tearing my hair out for over a month trying to find a stock ROM, Kobo came to my aid.
I've been given permission to share it, so if anyone else ends up in a similar bind you can download it here:
https://mega.co.nz/#!74o3BSaa!08uTD6...gXLwaLU-bWtaaU
http://www.mediafire.com/download/6n...an-ota-932.zip
As I couldn't enable USB debugging ADB would not detect the device using stock recovery. I had to sideload it:
Reboot into recovery mode and select the option to update using ADB sideload. ADB should now detect the device, but only allows sideloading.
Copy the .zip into your ADB directory.
Copy and paste this into your shell window:
adb sideload macallan-ota-932.zip
The device should then automatically start updating. After it's finished your device should be as it was out of the box (or maybe a few updates later/earlier depending on when you bought it).
This method also works using CWM if you're using that instead of stock. You'll be given an option before reboot to prevent CWM being over-written by the stock recovery.