You need to go through a certification process to legally purchase and use that motor. You will also need to go to a launch that has an appropriately large field and has received FAA permission to launch such a large motor.
https://nar.org/hpcert/NARhprintro.html and
https://tripoli.org/ (look under "documents" and then "certification" and then "how to certify") will give you an overview of the process.
You really really need to find a local club that will mentor you!!! They'll also be able to put you in touch with motor vendors, once you're ready.