Don't panic, first you can see where they're using find or locate or by searching in http://slackware.com/pb.
The latest will also tell you in which package they're, in this case http://www.slackware.com/pb/searchfi...Fshutdown&w=on
will tell you it's on sysvinit package.
Now you can see if you've that package using pkgtool or running this command:
If you see a line, then you've it, else, you'll need to get it, you can use your slackware cd or download it from that address.
If you have the binaries, then maybe your path has changed, you can see that with:
In that case the problem could be that your /etc/profile file changed.