If you buy a Delorean and a working Flux Capacitor off eBay, and get the car up to 88 miles an hour, you could hit the late 80's and just buy a non-restricted AR-15 with your $10 FAC. (ah the good old days....)
Fantasy of time travel aside, if your purchasing an AR-15 style carbine for training purposes I'll assume that your going to be working with an AR platform as well. That said, what is the purpose of it being non-restricted? If your going to the range to practice techniques to save your bacon when involved in a ballistic event, then the status of the rifle shouldn't matter as much as how closely it would replicate what you'd be using, um... at work so to speak.
For myself, the Non-Restricted "Black Rifles" I have are used for hunting and plinking. All of them are quite dissimilar to my "working guns", but the core techniques I employ are the same regardless of the platform I'm using.
Good luck in your quest.
M