Several TeaChatters who drink Chinese greens and are picky about them feel that TeaSpring has pretty consistent quality in greens. They currently carry three: http://www.teaspring.com/Dong-Ting-Bi-Luo-Chun.asp
. I haven't tried greens at TeaCuppa, though they have a fine reputation for Wuyi oolongs. In addition to TeaSpring, I have had high quality greens from Dragon Tea House, Jing Tea Shop (the one in China, not the one in the UK), and Yunnan Sourcing. A couple years ago I had the Pi Lo Chun (Green Snail Spring) (ZG 92) from Upton that I enjoyed quite a bit then, but haven't ordered from them since. In fact, it was my first Chinese green. It's been a long time and I have learned a lot about tea since then and I could easily be mistaken, but I have the feeling that the other referenced shops are more likely to provide a higher quality and fresher product.
If you are doing a web search, you may have better luck with the Pinyin transliteration: Bi Luo Chun.
There were a couple nice review articles about Chinese greens in Cha Dao about a year ago that you might find helpful:
http://chadao.blogspot.com/search?q=Thi ... furnished+
http://chadao.blogspot.com/search?q=Fil ... %29+Spaces
The first, by Geraldo, is especially nice because it reveiws quite a number of vendors and greens. The second, by Anodyne, covers just Bi Luo Chun.