As the above posts have it, only a full-auto capable rifle sold to the police or military is "mil-spec".
However, about as close as you can get in a civilian legal AR-15 series is the Colt LE6920 M4 carbine.
Colt builds these using the same parts as used on military sales rifles, except the commercial LE6920 M4 has a semi-auto lower and a legal length 16 inch barrel.
Other than that, everything is the same, made of the same parts and used in commercial and military sales rifles.
Visitors who've gotten Colt plant tours witnessed Colt making parts like uppers, bolts, bolt carriers, and barrels from the exact same raw materials on the same machines for commercial and military M4's.
As example visitors saw bolts and bolt carriers coming out of the machines and some going to commercial rifles and some going to military rifles.
Same parts, made on the same machines.
Why Colt is the closest to genuine military specifications is because Colt doesn't try to run two parts streams, one for commercial and one for military and police.
That means that Colt just uses the same parts for both commercial and military rifles.
All parts are made to a minimum of the mil-spec.
That doesn't mean they barely meet the spec, it means that they're at least equal to the spec, and Colt says all parts exceed the spec.
What "mil-spec" means is that EVERY pin, screw, spring, bolt, barrel, stock, etc, MUST meet the military spec.
Each and EVERY part in the Colt has to meet the mil-spec and while Colt buys parts like magazines, stocks, pins, springs, screws etc, from outside contractors, each part must be made to the mil-spec, and the supplier must provide Colt with legal documentation and lab tests swearing that the parts meet the spec.
Colt in turn has to furnish that documentation to the government.
Other makers who don't sell to the military are completely free to use mil-spec or NO spec, since they're under no legal constraint to meet a military specification.
What that means is that a higher end supplier may use parts made of metal better then the Colt mil-spec and made to a higher standard. Some makers do have what they say are parts like bolts made of steels and heat treating that are better then what the mil-spec calls for.
However, they don't have to use mil-spec parts like springs, screws, pins, and other small parts.
Where Colt's parts are made by American contractors, other makers are completely free to buy screws, pins, and other parts in China or Pakistan if they want.
Again, they can use whatever specification and quality for their rifles and small parts they want and they don't have to prove anything to anybody, like Colt does.
You can buy higher end rifles made of mostly better then mil-spec parts but all parts may not be mil-spec quality. As long as the maker is satisfied that the parts will stand up, they can use them.
So, if you want a rifle in which all parts are made to the military specifications, Colt's LE6920 M4 is it.
You can buy lower quality rifles and higher quality, but the Colt M4 is as close as you can get to a military M4.
