Adam S, IMO, made the hardest part of Big Baby available to anyone already. The rest can be built from found parts. One trip to a PVC pipe supplier will get you the bulk of the gun portion, while online searching for a correct wooden gun butt will get you that piece. Hell if all else fails, a resin casting of a sculpt will work as well. I know I personally want a Big Baby done that way, and plan to do so very soon.
I would be more than happy to share any progress photos, so that others can either tell me how ****ty it is, or follow my build into their own.