CPC farnell..... but I suggest you don't waste your time on it and buy a decent panel,
The ADE accenta is a popular DIY panel but you should consider one of the 7or16 zoned scantronic panels.The scantronic 9448 is a good graded panel albeit only seven zones and very easy to install and program.
Buying a new transformer for an old panel isn't really the best course of action and chances are you won't get one that's suitable regarding voltages, or without the need to mod the board to suit a spurious one.
e manno, February 2013