The closest to you would be: https://www.pronghornev.com or http://www.overlandadventuretruck.com/slide-in-truck-campers/
Big shout out to Pronghorn! They did both the construction of our box and CAD drawings of the interior layout. The drive to Alberta from the Southwest was a bit, but I don't know who among us wouldn't be up for a road trip. In addition, there is an advantage to US buyers purchasing in CAD.