Depends why they wanted the Sub-Sonic Ammo. It has other uses, than just for silenced weapons.
The slugs are often larger and more unstable. I am just guessing here, but for a “Trench Broom” such as the Long Lugers or similar from WW1, short range but an instant effect could be required. Also handy in Urban Ops, where the risks of Supersonic rounds bouncing of walls, etc goes up.
Likewise, the slaughter of Jews and other prisoners (which at the start of the war was largely done by gunfire, rather than the gasses used for the later “industrial” scale killings. Would also have benefited from such ammunition. Likewise anystray rounds wouldn’t travel to far, and the risks of richochet are reduced.
The only large scale sileneced weapons I know of were the Sten and the Welrod, some of the Stens were produced in other countries including Poland, and a Carbine which was used in the Jungle alot and by Commandos (the De Lyle).
The Welrod was a 9mm pistol (single shot), all had fixed silencers that were part of the barrel and none removable. The Sten featured a canvass wrap around the barrel and silencer because of the heat it would build up during firing.
The Germans used captured silenced weapons, but I am not sure if they manufactured their own in any great numbers. The Sten Mk IIS (silenced mk 2s) even had a German designation (they must ahve been that prolific) of MP.751e. (All captured Stens were labeld MP.75(digit)e.
The Stens, Welrods and De lyles used the baffled silencer method.
The Germans seem to have relyed on add on silencers for their silencing requirments, but even they were rare. However it highly likly, that bar a few specialised units of commandos, that the Germans never saw a need for them. And the captured Sten MkIIS’ may well have filled their requirements admirably. These were actually the most common silenced weapons used by the Germans.
I have found mention of the following weapons having add on silencers (albeit often rare examples or only prototypes), list below,
P-08 (add on silencer);pictures prove that it existed
Walther PP and PPK (add on silencer) pictures prove that it existed
P-38 were built after the war
Revolver 612(r) [Nagant 1885]: (add on silencer) prototype only, research carried out by the “SS-Waffenakademie”
G43: all G43 produced from mid-1944 onwards were fitted to use a suppressor, very rare.
K98K: rebuilt Soviet S-40 silencer
The following had fitted silencers
Steyr M12/M16 machine pistol used by the Brandenburgers (heavily cutdown version of the M12 and reduced capacity magazine)
Mp-40:prototype only
Kommando-Karabiner: special rifle with the silencer of the Mp 751(e)(the Sten MKIIS 1000ydstare), only four Karabiner built, but did see service.
The Germans didn’t really go in for clandestine ops to the same level as teh British (including the various Resistance Movements in the occupied countries). Likewise, assasinations inside Germanys reach was really the job of the SS or Gestapo, who didn’t really go in for the subtleties of the silenced weapon.
All of their attempts to silence weapons appear to be reengineering of British (mainly) weapons and at least one from Russia.
The British mainly went in for the baffles, as previously mentioned. The Russians seem to have favoured this method also. So at a guess, I would say the baffles is the way to go for a silenced German replica.