Great work there, Andrew
![thumb ^^^](http://www.aussiepinball.com.au/Smileys/classic/thumb.gif)
Speaker - Try JB Hi Fi or similar ? I've never had to replace one of these before, but a cheap speaker should do the trick.
Here's a good link providing an insight into speaker selection for DMDs - as long as you follow the 8 Ohm limit you should be fine.
http://www.thekorn.net/speakers/