It is indeed a RebelScum.com exclusive, available here:
http://stage.rebelscum.com/estore/products.asp?cat=177
It was originally $65 from RS, but has recently been dropped to $55 + s/h. I'm not sure about prices via other stores or GG, which I don't think include the signed photo.
It's also been available via other outlets, but without the signed photo.
As for getting it directly from GG, it is available but you must be a PGM to get it from them.