I dont think there is any, I know there is a "Law" for possesing but I dont remember anything about selling or buying, you can get them at Cabela's and I seriously doubt they check to make sure you are LEO/Firefighter/Paramedic.
But I dont own one or have tried to buy one so I DUNO.
You can get automatic or assisted opening at Cabela's?
Swithchblades are illegal.
I love my auto knives... the kershaw assisted openers are just as fast but I had 3 and they did not hold up like my higher end autos, I usually got 6-8 months out of one from $30 to $60 a pop.
My SOG-Tac Auto is going on 1.5 years of daily carry including on duty, bargain at $120. In February I got a Microtech UTX-70 OTF that is my dress/light use knife and it is flawless and silly fun to play with.