1st 2 albums were self-released and, therefore, they hold total control over them and only sell physical versions on their website. Error was from a label but is odd that it also can only be bought through them.
The new album is available everywhere, plus they have signed copies through their store. I bought the vinyl and CD from Amazon, well, pre-ordered. Then I picked up a 'Pau Edition' of the special signed version from them.
If anything is currently out of stock at their store, it will eventually come back in stock.