Join a club! The club typically has the waiver for larger birds. I drive an hour for mine (and cross the US border to do so!) otherwise it's at least a 2 hr drive to the next closest field. And, you'll need to join either NAR or Tripoli for the club.. NAR is typically lower power, whereas Tripoli is typically higher power & experimental.
You'll need your Level 1 when you get to: models larger than 1.5kg, 62.5g of propellant, and 160N total thrust. Anything over these needs L1 and / or an FAA waiver. (A G64 has over 62.5g or propellant, hence it's considered a 'high power' motor) And you'll need your L1 to buy larger motors..
Most will start with Aerotech Motors, then switch over to Cesseroni as they get more involved. Madcow have an excellent array of kits to choose from, many well suited to an L1 or L2 attempt. (And Mike is easy to talk to!) Also look at LOC/Precision and Binder Designs.