I got Source Unpack from the Source Runs website, but it doesn't contain the Portal.cmd file. I used the Unarchiver to open it and I am on a Mac. Any advice?

Get the source unpack in the "Resources" tab here not at the website

My unpack didn't have a cmd either, but it came with a bat file that worked the same.

I got Source Unpack from the same site as the one in the resources tab and I can't run .bat files on Mac. It might just not be possible to play Source Unpack on Mac.

Source unpack runs just fine in A WINE

If there is no file at all it is most probably an antivirus thing