Is there a substitute for dry frosting mix?

I found a great cookbook from 1971 produced by Betty Crocker and several of the recipes require dry white frosting mix. Unfortunately Betty doesn't make that product anymore. Is there a substitute? I've looked online and found that neither Pillsbury or Jiffy makes it either. I was really excited to try out some of these recipes---thought I'd made a great find but now disappointed that I can't find ingredients. Please help!