If you must have milk chocolate, there are a few rice milk based chocolate bars popping up on the market. The soy-based ones didn't go over, but the rice ones seem to be popular. Vegan Organica (U.K.) and Terra Nostra (Canada, U.S). are two leaders in the rice milk chocolate market. Both companies also make milk chocolate bars, so these may not be suitable for the highly allergic due to potential cross-contamination.
Ingredients, processes and products are subject to change by the manufacturer at any time. All products should be considered at risk for milk cross-contamination. Always contact the manufacturer prior to consumption.