You might also want to take a look at the "clone" command we have here: http://github.com/BenPhegan/NuGet.Extensions
Supports similar functionality, but you can clone from one repo to another using:
1) Full clone of the entire repo
2) Partial clone based on a package
3) Partial clone based on tags (i.e. all "external" or "nunit" tagged packages)
4) A "refresh" mode which gets any new package versions for versions already on the feed (useful for "mirroring" other feeds)
Might be some things that you could use as well.