Soy/Rice Milk Powder Substitute

[star_lace]

I recently purchased the Babycakes cookbook and now I have a question. The frosting recipes call for soy milk powder. I'm allergic to soy and the book says that you can substitute rice milk powder. I can't seem to find this at my local health food stores and though I'm sure I can find it online, I was hoping to bake this weekend. Does anyone know if there's an alternative I can use? I substitute stuff all the time in cooking, but I'm always terrified to do so with baking especially when I'm unfamiliar with the ingredients. Anyone have experience with this or recommendations? On the chance that I can't find rice milk powder, does anyone have a good frosting recipe that is sugar and soy free?

Also, does anyone know of an online store that sells xanthan gum for a reasonable price? Most of the recipes in Babycakes call for less than a teaspoon, but a small bag at my Whole Foods was $12.99 and I'm having trouble justifying that for the few teaspoons I'm going to need!

Thanks in advance.