Well I guess I get to use my useless airsoft knowledge here.
A company has made a BAR, JAC of Japan. They do cost $1200, IF you can find one. I know of 2 floating around in the United States. This is a gas piece, and a beast indeed. 18 pounds (just like the real thing) of steel and wood. Spec'd for very high pressures too.
The M1 Garand exists too, made by Smokey's I believe. Very rare piece indeed, Smokey's usually makes limited runs of their guns. 100 pieces or so is not uncommon. The price is also usually upwards of several thousand dollars. This one is also gas. Not sure where they butchered the system from, but it's almost guaranteed to be an NBB ,which are better anyways.
The electric M14 does exist as well, although the gas M14 does not, to the best of my knowledge (and I would know if one did). Nemoto Gun Works makes the electric M14, it's a custom job that uses an AUG gearbox (butchered for use in the M14). It's based off of a model gun M14, the Hobby Fix I believe. The gun cannot be field stripped, if it breaks you have to send it back to Nemoto for them to repair it. The price is a mere $2500. I've talked to a guy who owns one, so my info is accurate.
Wow...I may not really be too good with the technical side or even a very good player, but I know my useless airsoft trivia.
1. Ninjas are mammals.
2. Ninjas fight ALL the time.
3. The purpose of the ninja is to flip out and kill people.