to my best knowledge, setpatch patches some things in the OS which might not be in ROM (last minute fixes?), you could maybe survive without setpatch but it's definitely a good thing to have. Setpatch resides in the C drawer of the Workbench disk. The C drawer holds almost all commands which is used by AmigaDOS such as copy, dir (I think) and so on.
You could always boot up your Workbench disk, go into the C directory and see if you can see the file when you type dir. This is simply done by typing:
cd df0:c/
dir
If you see the file you should be able to copy it to your hd with the copy command
copy df0:c/setpatch dh0:c/setpatch
I hope this helps
