My apologies if you've come to this page and found no listings.  Unfortunately, it's not unusual. 

It's extremely difficult to find batas de cola for sale ready-made.  These dresses are much more difficult and expensive to make than a regular flamenco dress.  Also, demand is lower because only experienced dancers are really capable of dancing in them.  So it's not surprising costume manufacturers are reluctant to produce them on spec, but prefer to wait until they have an order.

If you want a bata de cola for practice, your best bet is to buy one second-hand.  Otherwise, it's likely you will have to get one custom-made.