I don't know if any of the 30 colorways were unreleased, but if so then there couldn't have been many. The October Toys website lists 20 colorways and who they were sold by.
Of the ten remaining colorways, two were sold at the 2013 SDCC, one was a second run of the flesh colorway sold by the distributor, and one is currently being sold by Mini-Figure Militia.
That means only the following six colorways could possibly have been unreleased: red, tarred color change, bruiser color change, holly berry, winter blues and butter.
The October Toys website lists winter blues as a series 1 colorway sold by Onell Design (it calls it "light blue"). A sleeved series 2 in this same colorway recently sold on ebay. So I would imagine Onell Design sold this same colorway for series 2, and the October Toys website wasn't updated properly.
Similarly, the October Toys website lists bruiser color change as a series 1 colorway sold by 3DRetro (it calls it "color change Blue 320C to Red 185C"). So I'm guessing 3DRetro also sold this colorway for series 2.
As for the remaining four colorways, your guess is as good as mine. Maybe they were unreleased. I was able to obtain all four of them, but only for the Grimm Gourd figure (not the complete sets).
Edited by mulder2019, 17 September 2019 - 11:29 AM.