Those are called headpins. You can get inexpensive (not high quality) ones at Michaels or other craft store. If you want to make higher quality jewelry, I recommend one of these online sites to get your findings: www.artbeads.com www.fusionbeads.com ...
Well, peridot is more of a yellow green and emeralds are darker, so it depends what you like. Peridot is definitely more affordable.
what kind of pendants are you looking for and what are your goal price and your buying quantity? if you want to buy them in bulk from china, you can contact me for that.