I bought the base game, but the store's page shows two available DLCs: Complete rework and Unrated DLC. Clicking on each of them leads me nowhere (top store page with all games), and clicking on "add to order" does nothing (no items appear on the order list).

Any ideas: is it my location restriction, or are these DLCs unavailable in GOG?

Seems like location restriction, mate.

It's definitely location restriction

Yeap seems it was the location issue on my side.