Ive managed to find a 3925-B10B off ebay, new and unopened.
Currently just playing around with it and exploring menus, it's not immediately obvious that I can use it in modem/router mode to connect to Sky Fibre Pro (MER Option 61), is that expected? I can only see PPoA for ADSL and PPoE for VSDL. I've tried using suggested abcdefgh@skydsl and a few numbers for a password, however I think it needs to be set to MER with a client identifier ID and Vendor class ID Inputted, which isnt visible.
To be honest, i dont plan to use it in this manor, it'll be set to bridge mode and i'll be using a seperate router however i wanted to connect to the internet with it and just have a play as well as update the firmware.
I cant find what firmware version its on and 'Firmware Update' isnt an option from within the maintenance menu but for now ive assumed that might be visible once an internet connection is established.