If you're looking for a Carnegiea Gigantea--and I don't mean the WWE wrestler who goes by the same name--you pretty much have to come to Arizona. Or Mexico. Yeah, there's a few stragglers in California. Good luck finding them on your AAA map. So unless you direct your Art Department to 3D print a saguaro, this is the place.
Saguaros are so iconic that Tucson sent a specimen to Amazon to lure them to Southern Arizona. Sort of like one of those cacti-in-a-box you can get at the gas station, except 21 feet taller. And even though Hollywood has mostly forsaken Tucson when it comes to shoot'em ups, international fashion shoots still love the desert. UK-based TOAST shot its new spring line around Tucson last fall, and, sure enough, scroll down here and you'll find saguaros.
My own example (above) guards the hills and ravines of Sweetwater Preserve, west of Tucson. It was one of those rare, rainy days when you have about six seconds of sun to frame your shot and not trip over an ocotillo. If Reg Manning were drawing this saguaro, it would have a cowboy hat and say, "Howdy."
And no, Mr. Bezos, you can't have it. That was a one-time offer.