where can i purchase this to grow?

A quick Google search shows some vendors offering it (interesting plant, for sure!). Don't see any mail order outlets off hand, though. What area are you in? I see it mostly offered on the west coast.

There was a discussion a while back...here:
The thread "Wanted: Dianthus barbartus Green Trick seeds" in Plant and Seed Trading forum

I recently saw some for sale in the floral section of my local Kroger grocery store. Maybe you can buy some and try to propagate from cuttings?

Are Green Ball and Green Trick the same plant?

Edit: Ha. Answered my own question. Apparently they are very similar, but the Green Trick has a flatter bloom.