At this present moment there's no official way to play Chapter 2 outside of Patreon, since it's still in rapid development and being able to test the alpha as it evolves each month is more a perk of that specific tier than outright being a means to 'buy' it. Which I know is less than ideal and can understand the enthusiasm for wanting to play the game--but am not sure if there would be a good way to handle one time purchases for the alpha and wouldn't want to mislead people into what they were potentially buying while things are still so heavily in the works.
Will the finished version be purchasable outside of Patreon? Maybe on Itch or something? I've been wanting to play this forever and it'd suck if my stupid card blocked me.
Not to worry! Once Chapter Two officially releases it'll be on all the usual channels like before (itch.io, Nutaku, Mangagamer, JastUSA, etc.) so you'll have plenty of venues to choose from when buying it!