Each state has their own logo but there appearently is a national one.
http://www.ccesaratoga.org/ima...
The problem with logos is you might encounter legal issues. For a generic MG badge, any garden related image such as, rake, trowel, potted plant etc. with the letters MG would do. I like Ken's idea for individual state images with MG. For the orchid and plumeria societies, maybe use the current badge images with the societys initial added over the image.