When I made my 17 cosplay, I did those green socks like this:
1. Go and buy some green fabric.
2. Sew two "tubes", that look like socks without foots, from that fabric.
3. Put the tubes on your legs and put the lower edges of the tubes into your shoes.
Well my explanation sounds very stupid but it works if you don't find suitable socks. If interested, go and look my 17 cosplay from my gallery so you see how I did it.
I hope this helps.
to my surprise, with half closed eyes things looked even better than when they were opened