Are there any subguns available in .40 S&W?
I know the MP5 is available in 10mm. I think I would stay away from a pistol caliber subgun altogether and arm my SWAT team with M4s in 5.56mm.
Maybe we should ask if the sun has set on the pistol caliber submachine gun. What application for either 9mm or 40 S&W or 10mm couldn't be done with 5.56mm? Considering the penetration tests show that 5.56mm may be preferable for indoor use, the bullet breaks up better in standard building materials thus is better where over penetraion is an issue.
I think suppressed weapons in a hostile environment (meth lab) is the last tactical function for pistol caliber submachine guns.