You can create a new "Obsolete" folder in the vault, move the files to the new folder. If Admin, you can change the folder so others can not view it.
In the obsolete state only have admin permissions. That way you don't have to worry about folder permissions. The designers won't be able to search for/use them out of the explorer.....
The parts will show up as suppressed in the assembly. I put the stop sign symbol as the state picture for a visual clue.
It doesn't seem like you can have it both ways.
In addition to the permissions and states, you can add a feature to the model that makes it very clear that the part should not be used. I typically add some extruded text with something like 'OBSOLETE - USE PART XXX.SLDPRT'. It is large and very visible and will make a mess of any drawing or assembly where the part is added. Having the pointer to the correct part makes it easy for users to replace it with the correct component.