Freeman Manufacturing Supply has a video library that is a free how-to regarding mold making, casting and laminating. They also sell a variety of sample kits and other supplies. Their video collect has over 2 hours of content, plus their technical library has some useful resources as well. These resources include a glossary of plastic tooling terms, shore hardness guidelines, viscosity guidelines, and conversion tables. Another section of their site has a variety of users guides, such as one on selecting the right adhesive.
One line of their products is called Renshape and is polyurethane foamboard for machining. This line seems intriguing for machining via the CNC machine.
Last but not least they have some alternative lumber products like a pre-primed white Masonite sheet and "armorboard" an exterior grade plywood with hardboard faces.