The full game is currently planned to be for sale on Itch.io and Steam. It is likely that there will be a new Itch.io page for the full version when it is released though.
December 16th report. Check-in on SpunkStock's status. Starting on next game's prototype. » Comments
If the reason you're planning to make a new Itch.io page for the full version is that you want to leave the free version available for free, then there's a solution to that:
I don't know the details of how (since I've never uploaded anything to Itch.io), but I know it's possible to have some of the files in a title locked behind a certain price, while leaving other files accessible for any price. This would let you leave the 0.12 version up for free while making it so people would have to pay for the full version.
Yeah, you can have different files/packages sold separately within the same page. There is an issue with it though. It's a bit weird, but considering the SpunkStock Demo was a part of a free bundle at certain points, when a game is claimed via a bundle, you essentially "claim" the whole page's contents, as opposed to specific files/packages. This means that anyone who has claimed this game via a free demo bundle in the past will have access to any files on this page (Even if I uploaded the full version after the fact).
From what I understand, this is how it works at least.