Unfortunately, we are all other users here and do not know how Apple handles availability/inventory of items that are sold in their store. So, you will have to contact the Apple store.
Having said that - in general, my experience has been that any item that is "currently unavailable" may no longer be available/has been discontinued.
However, it appears to be available from the mfr:
http://www.brenthaven.com/products/collins-slim-brief-laptop-case?gclid=CNTC78m5 8coCFQMQaQodf38H6A