You can look into hobby shops or cake decorating/chocolate making shops or website.
We actually used food grade silicone for our cake decorating molds. The finished product is a bit rubbery. This is an example of the food grade silicone mold making kit at our local Michaels (a craft store):
EasyMold Silicone Putty
<I've seen liquid kits (rather than putty) on the web ... depending on application, one or the other might be easier to use.>
For something that is hard .. try acrylic resins (they make custom jewelry with it, although the resins are not marked food grade.) You might find that in a plastic supply shop as thick acrylic resin is what you use to bond & fill acrylic. This is an example from Michaels:
Castin' Craft Clear Polyster Casting Resin with Catalyst
<That is actually a polyester resin - you can find acrylic resins as well. PS - no idea how well either type will work ...>
Note - not an endorsement of the store ... just some nice pics for you.