You should have them in your PC, maybe try validating steam. I can provide the files worst case but you should be able to get them pretty easily yourself. Or why don't you just install steam client on your Windows server and then do the system variable or just drop them in. I don't really like this method of dropping the files in win64 as these files get updated sometimes with steam updates and I'm not sure what issues would occur on the game servers in the future running outdated versions. Maybe nothing, I don't know.
Also if you planned on using metamod and counterstrikesharp then I think you actually don't need the 3 dll files mentioned above, as metamod and css fix this themselves.