Where can I find weapon silencers in Deus Ex: Human Revolution?

I knew there was a shop in the first city hub that sold them, but a quick check on the wikia page gives a fuller breakdown:

• Purchasable at from Seurat in the Detroit Apartments 2nd floor (accessible through fire escape by the basketball court).
• Purchasable in Hung Hua Hotel 1st floor.
• Found in a drawer in Montreal - Online News Division (Level 3).
• Quest reward from Smash the State (Act 4) Detroit by Knocking out target "White" instead of killing him.

This doesn't seem like many, but they can only be used on the 10mm Pistol, Combat Rifle and Machine Pistol anyway.