For myself, what really helped was working at an office where everyone's pictures were up on one of the walls. Going to the restroom meant passing the pictures. There were about 30 people there.

At my current office, there is a staff "phonebook" that also uses people's ID badge photo. At this agency, there are about 400 people working here. Plus about 300 more seasonal staff in the "busy season".

If there are "team" photos, see if you can get one and write names on it. You'll get a lot less static from HR if you let them know you have a hard time remembering names and ask them to help you write the names down.