Is there an extension for the Stock/Buffer Tube made?
Not that I’ve ever seen. My two guesses are: longer length would affect the compact folding feature of the gun and the tube internals would have to be reworked to make it work - adding extra cost and making it incompatible with the standard gun.
I personally like the carbine length. How much longer of an extension do you want? Why do you think its needed?
The bolt tube is the serialized part of the Gen 2, so I doubt a tube replacement will happen.
That said, MCARBO makes an extension that adds about 3/4" LOP. Missouri Tactical makes a pad that get you near an inch. And, I can go stupid long with my MFT Minimalist installed. Plus an inch is as short as I can adjust it without charging handle interference (unless I start cutting off the front of the minimalist.
Searches on terms like buttstock, pad, recoil an LOP will get you 'bout 20 threads worth of discussion and show and tell.