How to download pre-built binaries from MacPorts without installing?
Macports guide says 


  MacPorts can pre-compile ports into binaries so applications need not be compiled when installing on a target system. MacPorts may create two types of binaries: archives and packages.


However I found issues with packages a few years ago (which might have been fixed) and the following is more of how I view MacPorts.

If MacPorts does have a binary package which it does in most cases then it behaves exactly as a package install including man pages. The only difference is that you need the command line compiler and the MacPorts sources (not the sources of the packages) installed and that the code is in /opt/local.

Also due to shared libraries you can't just take an executable and run it it probably depends on other shared libraries which MacPorts also provides.

As for centralisation you could easily install on one machine and then rsync or rdist to all the others (or use other macOS replication mechanisms) or as MacPorts pointed out set up a local repo.