Soy Protein Isolate
This is a common product at health food stores, co-ops and also bodybuilding health and vitamin stores. The key is to check the ingredients. You want Soy Protein Isolate 90% or as close to 90% as you can get. 90% seems to be the standard to be called soy protein isolate. Don't buy soy shake mixes. You want the pure stuff.
One pound of Genutine will make 32 batches of marshmallows! Woo hoo! It works great but if you want to try and recreate it yourself, it will be much more expensive. If you want to give it a shot, here is my best guess at the Genutine mix.
Locust Bean Gum
Acacia Gum, also called Arabic Gum or Gum Arabica
Carrageenan (Kappa, not Iota)
Kappa is used for stronger gels. Iota is used for softer gels. You want Kappa.