I purchase metals through certified mills only, insuring that your jewelry is made from ethically mined metal only. 
 I use ArtResin and it's been evaluated by a certified toxicologist at the American Society for Testing and Materials as being non-toxic when used as directed (conforms to ASTM D4236). It is formulated using the highest quality materials and therefore produces no VOCs or fumes. It is a clean system, meaning there are no solvents or non-reactive diluents—everything in it reacts so nothing is free to become airborne and cause health issues. It is also non-flammable in its liquid form. For all these reasons, it is therefore classified as a non-hazardous material and is shippable by air. Furthermore, many curatives have a powerful odor, however ArtResin has only a low odor and is applicator friendly.
I collect most of the plants on my adventures, making sure I never over pick from the bush im taking from. I keep the fauna in mind, always remembering the butterflies, insects and food chain of nature. 
Anything I can't find on my own I'll find at local flower shops or online pressed flower shops (my favorite are from Utah!)