There are no official repositories right now, but AlexT created this amazing unofficial repo: Index of /edison/repo, and here: Edison Package Repo Configuration Instructions you will find an explanation on how to install packages from this repo.
However I suggest you to use "opkg install" instead of "opkg upgrade" because if you use the later the Edison will upgrade all upgradable packages, this could lead to your Edison's memory to be filled up very quickly. I suggest you to only install the packages you need in order to avoid what I explained before.
So, the commands you use should look like this:
opkg update opkg install perl
Thank you Peter,
I'll check out AlexT's repo.