The backs of old photographs make good pallettes. They dont absorb paint and are a matte white, letting you see the paint well. I use them alot for all sorts of things besides paint mixing, like dabbing super glue etc.
Also, thermoformed OTC medicine cells are dandy, as mentioned. I am lucky in that I am employed by a pharma firm and actually make them. For you, I'll send you some, if you PM me. Anything for a fellow NAVY man.