There is no earliest. Weapon attachments and mask items come from cards you pick at the end of each mission. You just have to be lucky enough to get silencer. --- Don't Blink. Blink and you're dead. Don't turn your back. Don't look away. And don't Blink. Good Luck.
I'm level 55 and the only silencer I have is the Ninja upgrade for my MP5. --- You are not entitled to your opinion. You are entitled to your informed opinion. No one is entitled to be ignorant. - Harlan Ellison