Can someone point me in the right direction for what classes I should use for a manual dependency loading system?

I’m attempting to bundle all modeling related files into one archive (tar/zip) so you don’t have to deal with 4 separate files all the time.

I’m not sure I understand the question. Do you want to load your model assets (3D mesh data, textures et c) in a zip file? If so, you will need to load it yourself (using URLLoader or equivalent), unzip the loaded data in AS3 and split it up into separate byte arrays that you then send to the Away3D loading framework using the loadData() methods on AssetLoader, AssetLibrary or Loader3D (depending on what kind of loading behavior you want.)

Think about whether this is really worth the effort. If you use a compressed enough model format (e.g. AWD2, with embedded textures) and/or GZIP HTTP compression for the transfer, the benefit of being able to load files more easily might actually outweigh any extra file size that the method may or may not add.