Without fear of contradiction, as a lifelong boot fitter, boot fit trainer/educator... I will give you the 2 most common factors in repeated boot fit fails...
1. If proper assessment of your foot shape and flexibility along with your strength, fitness, and ski technique and history was accomplished at any of the shops you tried, it would not matter what boot you ended up with. The number of failed attempts means that all of the shops have missed something functional with your foot size, shape, and mechanical function, or about how and where you ski. The fact that the only feedback you have received on this forum is different models, brands, sizes, and scanning, means that no one out here including you understand what’s going on with you.
2.Sorry to be the bearer of bad news ( and you all can hate on me in future posts ) however by your own story, it sure seems to me that everywhere you go, there you are. With the number of attempts made at different shops and fitters that have failed, the only thing they have in common is you, your feet and your story while in their precense. If you have seen the Seinfeld episode where Uncle Leo, Elaine, and Kramer all got blacklisted on the “national dr’s database“ as being “troublemakers” Perhaps the National bootfitters database is preceding you in all the shops you have tried or called? Would you consider finding a fitter in a foreign country? And yes, I believe I am the funniest boot fitter ever!!!
In all seriousness, There is something else going on if all of the attempts to date have failed. Clues to look for to solve your conundrum: somewhere you mentioned your size and weight, this will factor into the stiffness choice. Also on the subject of flex, your ankle range of motion determines pressure to your forefoot, if your ankle range of motion is low or locked, this will have big effect on your forefoot. Do you have issues with early fatigue of your quads or hamstring muscles? Is and were any of the “custom” foot beds built taking into consideration your arch flexibility, arch height, and forefoot mechanics? To answer these questions and determine if they are effecting your outcome is where the best fitters play. Any ski shop can tell you what a boots materials are, what the volume numbers on the box are, etc. Only a handful of boot fitters have the assessment and problem solving skills for certain humans with hard to fit feet and mechanics. Along with the above thoughts, there may be issues specific to you around the nerve/blood flow pathways that cannot be explained by sizing, flex, or volume that is described by the boot supplier or the shop fitters. Once again there are very few great fitters that know how to swim upstream to find impingement on nerves and blood flow.
For the good boot shops you have visited and the money you have spent, IMHO you have clearly fallen through the cracks of legit boot fitting.