I have produced a new example for my Entropy library that performs precisely this function. The code was designed to be easy to understand, rather than fast, so it is a little unrefined, but should give a good starting point for your risk board. It currently has two multiplexed six-sided dice represented as seven led's for each die. More dice can easily be added. The example, along with schematic and statistical analysis of the code's performance is available from Google Code Archive - Long-term storage for Google Code Project Hosting. and I made a short video of my wire wrapped prototype to show how it functions, available from Google Code Archive - Long-term storage for Google Code Project Hosting.
Before publishing, I ran a test of about 12,000 throws of the dice (used another arduino to 'push' the roll button and record the results. Like all of the other tests (http://arduino.cc/forum/index.php/topic,108380.30.html) run so far, the performance is very good.
Hope this helps!