I assume the indicators cancel using a similar mechanism to other cars; a tab on the column or slip ring pushes the stalk back off as it passes over a lobe on the stalk switch.
It could be either the stalk switch or a broken/worn down tab on the slip ring/ column.
You might not get a definitive answer regarding replacing the stalk as it might not fix your issue.
My advice would be to take the cowl off and have a ganders at the stalk and slip ring.