I attempted to find a source for the statement on the wiki page for the wicked bad voodoo set, which states that the promotion has ended.
I started going through all of the patch notes, and I successfully determined that it probably happened before Febuary 24th 2015, assuming that it was documented in that wiki at all. However, there's a lot of patches. I have written a script that should look through all of them, but I'm bad at python, and it might not turn up anything. I'll edit if I find anything though.
Edit: I finished searching through the patch notes. There's no explicit reference to the promotion ending that I could find. However, in the June 20, 2013 patch, some files (dota_item_wicked_bad_voodoo_set.png, dota_item_wicked_bad_voodoo_set_large.png) were added to the econ folder which looks like the image being added to the store. This is the most likely contender for me for when the promotion either started or finished. Probably finished, but that's based off a gut feeling and wishful thinking.
Tl;Dr The promotion has ended.