Both the smc PENTAX-DA 21mm f/3.2 AL Limited (source) and HD PENTAX-DA 21mm f/3.2 AL Limited (source) lenses are listed as discontinued in Japan.
In the US, the HD PENTAX-DA 21mm f/3.2 lens is currently in stock at B&H and both lenses are no longer listed at Adorama.
More discontinued Pentax lenses can be found here.
