when there are not many choices, i would recommend that you lower your expectations.
when you walk into a ski shop as an adult with a size 21 foot that is high volume, a narrow heel, and large calfs, unfortunately your request will fall on deaf ears as there is the least likely chance in 98% of the shops out there that they would stock anything in a 21 adult boot. it's not a question of whether they will do you the service of special ordering a boot for you or not. it is the issues of first, is there any supplier that actually has one for sale, and secondly what are the chances that the boot they can get will fit you and ski well for you. with a size 21 foot and a desire to ski well, it is the most limited choice of product. the ski industry does not believe that you exist. which is why they do not manufacturer a boot for you.
in true 21's the tecnica 90 is still the only true 21 available. a few of the boot fitters on this forum know that and stock them. the lange is a 22 that they attempt to convert to a 21, which typically does not work for real 21 feet. the dalbello at least in sole length could claim that it is a 21, however it's internal last fits more like a 22.
so back to my point about managing your expectations, when you have very little choice, your best choice is to find a very good boot fitter that can help you make the necessary modifications to the boot that comes closest to matching your needs.