I’m guessing you’re using the link in the OP of this thread, because as far as I can tell, this item is no longer listed on teespring.
If I remember correctly, there was a moment a few months back when teespring did something to their store which resulted in a few items getting deleted from the sapien shop on teespring. Some of those other items had to be re-added by Team Dream. Perhaps this one was missed in that process.
In any event, your best bet would be to send a DM to @SammyG who will find a solution for you.