There are many items that are existing in game, but which you cannot obtain in survival mode, such as a fire block. There are other items such as nether warts which have a block (115 in this example) and an item (372) that have a similar name, but only the item is available. The block is marked red in the wiki’s item list. Until now, if you searched for netherwart in the shop, it would show you item 115, but if you tried to buy it, it would not have any sellers. However, plenty of 372 are in the shop.
To stop this confusion, the shop now will warn you if you try to /find or /search for an unavailable block. It will also tell you if you put up a purchase request for one of these.