If you go to a local dealer to order one, some, MIGHT give you lip about it.....
As stated, you can buy one yourself. Some sellers, like CMMG on this site, has the 7.5" DPMS Kitty Kat upper. Some manufactuers don't sell their uppers direct to "people", only dealers....and the Kitty Kat is one upper that DPMS will NOT sell direct, even though it is leagal.
At one time, some dealers required people to show a tax stamp to even ORDER a barrel less then 16". But I assume this was because of the BAN. Anything less then 16" would be a SBR and AR pistols (at least new builds) were illegal & you couldn't use a pre ban upper on a post ban weopon. Most uppers that short (7") were for pistols and the ads said "for pre ban pistol use"...... Now the ban is gone, but some dealers/companies do it just because.....