The only place the Transwarp beaming technique existed was the scrapped shuttle, Section 31 confiscated the lot and took it to their underground headquarters.
That was bombed, the only working model stolen by Khan, burned out and trashed in the crash and it's one way use. That leaves the Vengeance, she was totalled in another crash.
It's possible the equation no longer exists and the technology to recreate it mostly or completely gone.
Not quite true. The implication was that the equation allowed a clapped out old shuttle transporter to convert to transwarp beaming with no physical modification (such as boosted power to the sensors or confinements beam).
In the quasi canon comic (some elements of which made it into the movie), Scotty continued his research on the Enterprise until it was confiscated after he introduced a bio-hazard to Earth. In the comic he was able to use unmodified communications relays to shuttle the signal to its destination. It almost makes sense if there is a receiving pad for the signal to home in on but really the tech should not work as it is written.