Is there a package system (think
cpan, or even
homebrew) that would be suitable for shell scripts?
Shell scripts don't need much packaging, so most people use a source control system for this. There are dozens of options, but I'd start with github and come back with a more detailed question once the github / source control system broke under the strain of volume of your scripts or the complexity of the situation.
As it stands, we can only guess what your true requirements are since all three examples you list run natively on OS X and you can roll your own packages according to each recipe if you prefer to use them.