Just wondering...there are items on this site that Subeta has put out but when I go to search for them there are none available for purchase anywhere. How would I go about obtaining these items (the Kumos Tile for example), please?

It depends on the specific item. You can always try looking the item up on SubetaHQ or Subetalodge. is prize from the Tiles game

Try the advertising forums, someone might see your thread looking for specific items. But if none are available then you're looking at some serious sP.