I mentioned a couple of posts ago about how it's nearly impossible to find a dairy-free, non-nut-contaminated M&M substitute. I have now found one besides Whizzers -- it is called "Dark Chocolate Skippers" and is available through Vermont No-Nut Chocolates. Most of Vermont No-Nut's chocolates contain dairy, including their milk chocolate Skippers. However, they also make dark chocolate skippers that do not contain dairy as an ingredient -- but the ingredient list does caution that they may contain traces of milk protein, so try at your own risk. Ainsley had some because they came in the A&J Bakery Gingerbread House kit, and did not have a problem. She loved them. They come in bright colors like regular M&Ms (unlike Whizzers, which are much paler because they are colored without artificial ingredients).
You can order the dark chocolate Skippers here.