Being an engineer in high tech (higher tech than computers) I get a kick out of things that are considered "BIG SECRETS" that I think are just creative applications.
For foam cores I think a little experimenting will get you very far. Get info from the web on the marine foam applications. You should find a good amount of stuff on mixing these foams. Then try stuff.
I have been working on something that is a syntactic foam for a different use and that is what we did: a little research, get material, experiment and viola...
Here is what I am going to try: Get a limb-width board of, say, maple; mill a groove down the center that will be narrower than the final limb width. Mix and pour your foam into this groove; after it cures re-saw on the bandsaw and drumm sand to thickness just as if it were a regular limb lamination. Build the bow as usual. What could possibly go wrong? go wrong? go wrong?
The groove needs to be narrow enough that there is still wood at the sides of the limb after final shaping.
If I can stop working so much and get my garage shop fully pimped-out to make bows this is what I plan to do after I learn the basics of laminated bows. It should be great fun.
Invention is 10% inspiration and 90% persperation. Who said that? Ben Franklin, Thomas Jefferson? Wasn't me, but I have invented a few things and this statement is true.