'Green Giant' is a single cultivar. Suppliers pop up when you search for it online. If your State has a nurserymen's association with a web site you might be able to get some leads there. Oregon's association even has an online buyer's guide that lists suppliers by (selected) individual cultivars, my State has an buyer's guide too but tends to be limited to broader categories.

a little late responding but just saw this. I live in Michigan and bought from Advanced Tree Technologies in Indiana--they're on the web i think. They were helpful and we received our 53 (!) Green "Rockets" (i'm sure the same as Giant since the parents of this hybrid are the same) in fine shape. They've been planted now for over 4months and look great so far.

Hi...don't want to hijack the thread but the title of this discussion seems to indicate there might be "varieties" of Green Giant. I've wondered that myself because I've seen it listed as a 'thuja' but also as a 'cedar.' Anyone able to clarify this? Is one better than the other? Or am I totally confused?

Cedar is one of the common names used for Thuja, as well as other conifers (and even non-conifers) with aromatic wood. 'Green Giant' is a single hybrid variety, derived from the crossing of two species of arborvitaes (Thuja). Other cedars will be other species and varieties.