How do you get one?
Complete the game in 5 hours or less on normal difficulty to unlock a burst fire Samurai Edge with unlimited ammo.
Unlock "STARS Wesker" in mercenaries by getting an "A" grade on Prison. He's the only character who carries the Samurai Edge, which has a somewhat low capacity but great stopping power.
Tokyo Marui produces an airsoft model of the Standard Samurai Edge. This is what a majority of the STARS members carry. Chris' has a silver trigger and Jills' has a silver trigger and magazine.
Wesker had a slightly different one in REmake. The frame was silver and the grips were black rather then wood framed. Simple enough to build.
In RE5, Wesker carried a heavily customized Samurai Edge. Railed, full length dustcover, beavertail grip and the original wood-framed grips. It had an M3 or similar light on it in most scenes. The beavertail isn't produced in airsoft or IRL as far as I can tell, so this version isn't as feasible.