Not sure if you have a material preference... but the polertec fleece beanies they hand out like candy in the Army are definitely designed for big noggins. Like, maybe they expect us to wear them over the helmet? Not sure, but they are pretty big and come in foliage green.
I wear 7 5/8 - 7 3/4 hats and recently picked up a Peleton 240 beanie in the largest size available. Seems to fit my big head fine, but I haven't had a chance to field test it yet.
I have had good performance from an Icebreaker merino Flexi Chute in "beanie mode" for my 7 5/8 to 7 3/4" hat size (the ones I have are Max-1 camo, fwiw) ... it looks like Icebreaker's website lists a Realtree camo one on sale for $12 right now, fyi and in case you were interested.
... a Buff neck gaiter may also fit a large head in "beanie mode," but I have no first hand experience to speak to that option.