If you want to buy green colored contact lenses without prescription, you can get it online. I loved freshlook color contact lenses and they are very comfortable. Many of my friends get their regular clear contacts through freshlook. If you are in the United States, it is against federal law to purchase contact lenses without a written prescription from you doctor even you don't need corrective lenses. Any site that would sell you lenses without an Rx is a shady site.
Now colored contact lenses is no longer some rare products. You can even get at online shop. And i find some green contact lenses at http://www.eyesbright.com/fashion-and-beauty-contact-lenses/natural-coloured-contact-lenses/green-contact-lenses.aspx, varying in different styles. Aside from green contact lenses, you can also find Green 3 Tone Contact Lenses or Glamour Green Contact Lenses even more. Good luck.