The SCR is not technically an AR (since it is not strictly based on the Armalite design) and was designed for states with laws that prohibit guns based on their scary-looking appearance. In addition, to pistol grips, muzzle devices are also banned in those states, which is why the gun does not have them. If you bought the gun because of state laws, then it is likely you cannot legally have a threaded barrel or install a muzzle device.
In any case you have three choices for a threaded barrel:
1) Have a gunsmith thread your current barrel.
2) Since it appears to use an AR upper, you can most likely buy a new, threaded AR barrel and:
a. Have a gunsmith install it
b. Install it yourself with the proper tools.
3) Buy a different AR upper assembly (you will need to keep the SCR bolt carrier in a new assembly).