I am trying to find them on my Mac OS X Mountain Lion and it seems they do not exist. I do not think it is a problem of folders privileges.
Maybe it just doesn't exit and I have to create them.
It should be there as a character special file:
bash-3.2# cd /dev
bash-3.2# ls -l |grep null
crw-rw-rw- 1 root wheel 3, 2 Mar 8 11:04 null
Finder doesn't show these folders so you need to be in terminal to see them.
ls -leO / | grep dev
shows that it's hidden which you already knew. I wouldn't be surprised if Finder had a special case black list of places to not show, even when hidden files are presented.