Dafydd,
Yes.. from the acs-admin/install interface you can only install packages found on the openacs.org repo or locally.
But if you go to the Package Manager ( /acs-admin/apm ) at the bottom youll see some actions you can perform, among them : "Load a new package from a URL or local directory". This will take you to a form that allows you to specify a URL to a giving apm file, or, to a folder containing serverl apm files , or local path a apm file.
This way you could publish url's to your apm files and anyone interested would be able to install them via this interface.
