I've read that for the PS2 version of Metal Gear Solid 2: Sons of Liberty that the
USP Suppressor is not available in the US version in the Tanker stage. Has this changed for the HD version?
The USP suppressor is only available on your second playthrough of the Tanker Mission, on a save game file where you have already successfully completed it. It can be found on the tower that you can access just after the boss fight with Olga (go round the front out doors and there will be a ladder to your left), this is where the thermal goggles were on the first play through, if you found them.
I have the PS2 edition and the HD edition for 360, and I was able to find the USP suppressor at that spot on the 360.