Just to be clear, there are two different 'systems' here.
First, there are three 'DLC' packs that we (N3V/Auran) have created. First was the Blue Comet pack (US), second was the Duchess Class (UK), third was the PRR T-1 (US).
We are now also selling some payware assets from 3rd party groups. However, so far there are only two groups that have organised to have their content sold via our store, these being JointedRail (US) and Ocemy (China).
It's possible that a 3rd Party UK (or any other location for that matter) content creator may wish to sell payware via our store, in which case they can contact us.
However, we are limited by both our internal resources (for our own DLC's, which are listed above), and by the content released by 3rd party groups/creators via our store.