Can't find nether warts
Nether wart sometimes generates naturally in nether fortresses as a plant, in patches near stairwells.
Seems as though you are really just unlucky. They have a chance of spawning near every stairwell
Nether wart can be found in 19.0% of fortress chests in stacks of 3–7.
You may also find them in chests in the fortress
Source:https://minecraft.gamepedia.com/Nether_Wart