It is sold in the glues section at Home Depot, and the packaging is a cardboard baking with a tube of putty secured to the front. I don't recall the name, but I think the item is mostly green.
I'm using the Deltec putty now, which is simply awesome. It costs more, but it is pink like coralline, stays soft for several hours, is sticky and holds onto the rock as it should - I have zero complaints so far.
I saw Aaron using it when I was in Austin, so when I went to MACNA, I made a bee-line for the Deltec booth to buy some.