I bought a DMD Extender from Dr. Pinball to replace a broken DMD, but ended up being an easy fix on the display board. This unit will work in Bally/Williams or DataEast/Sega (but would need to fab a power adapter).
More info here. http://www.drpinball.co.uk/dmdextender.htm
Hopefully someone else can use it, and I can save you the shipping time from the UK.