https://www.auto-ordnance.com/auto-ordnance-m1-carbine/
Currently in production.
They fire a .30 caliber round, twice the mass of the standard 55 gr M193 5.56mm NATO round.
https://ammoseek.com/ammo/30-carbine
For a round that no one uses anymore, there sure are an awful lot of manufacturers making it and retailers selling it.
Some can see better results than that, with modern ammo and a little tuning. At any rate, nearly all mass shootings take place at point blank range. You've pointed out that the M1 Carbine has perfectly acceptable accuracy for that purpose.
The Hornady M1 Carbine FTX personal defense round has a muzzle energy of 977 ft/lbs. The Hornady 55 grain FMJ has a muzzle energy of 1282 ft/lbs. Compare either for purposes of mass murder to that of the most commonly used round, the 9mm, at 332 ft/lbs for the Hornady 9mm FTX defense round. For purposes of banning due to danger to mass shooting victims, looks like the M1 Carbine is just as deadly as the AR-15.
From just the first source that Google gave me, here are four different 30 round .30 caliber M1 Carbine magazines for sale. I presume that's what you mean by "banana clips".
https://www.cheaperthandirt.com/category/parts-and-accessories/magazines/m1-carbine.do
Shall we have TD add "they fire small caliber rounds", "they are not made anymore", "Nobody uses them anymore" and "banana clips" to his list of your lies?