Sorry, that was a typo when posting on here. I did originally run it as xxd:

    root@primus:/usr/ports # xxd
    xxd: Command not found.

edit:

It doesn't show up in my ports either:

    root@primus:/usr/ports # make search name=xxd
    Port:   textproc/xxdiff
    Moved:
    Date:   2013-07-26
    Reason: Has expired: Depends on Qt 3.x

    Port:   textproc/xxdiff-scripts
    Moved:
    Date:   2013-07-26
    Reason: Has expired: Depends on Qt 3.x

Obviously xxdiff is a different (if you pardon the pun) utility, but xxd should show up in that list also.

edit 2:

Another comment on here might explain why you're seeing xxd and I'm not: https://news.ycombinator.com/item?id=6360814 (it's not a separate utility, it's part of vim)

Since I didn't install vim on that box (just use basic vi), xxd wouldn't have installed as part of it. Where as in a jail on the same box, xxd does exist:

    root@primus:/usr/ports # which vim xxd
    vim: Command not found.
    xxd: Command not found.
    
    root@primus:/usr/ports # jexec 1 which vim xxd
    /usr/local/bin/vim
    /usr/local/bin/xxd

    $ whereis xxd
    xxd: /usr/local/bin/xxd /usr/local/man/man1/xxd.1.gz

I don't see xxd anywhere in my ports tree.

Haha... What a trip. This is the sort of thing that I'll end up wasting half a day trying to get an answer to.

You wont see it in your ports tree because it's part of vim:

    $ grep xxd /usr/ports/editors/vim/pkg-plist
    bin/xxd