It has unfortunately been discontinued.
https://community.smartthings.com/t/thingshield-to-be-discontinued-what-the-heck/64884?u=cr76
However do not fear I have developed a similar item for the ARM mbed platform and am going to port it to the Arduino over the Christmas period. So keep your eyes peeled. Here is the ARM project.
https://developer.mbed.org/users/Cameron/notebook/samsung-smartthings-mbed-development-platform/