Some time ago there was a site like that but the author discontinued its support. The only thing left for me was to make the simple script that reads xml data for every station and displays them together. Links to those xml data are not officially published so you need some knowledge or luck to find them.
The finished site is available here. It is updated every 5 minutes, so it may not be accurate during rush hours with many bike changes. Stations with zero available bikes are colored in pink.