Some of the OEM manufacturers make them.
But do you need them??? As much as I love them on target and err...."special" rifles, I wouldn't have them on a hunting rifle on a bet.
And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.