They are by invite only. As far as I know, actual employees of Estee Lauder Corporation are invited and allowed to invite guests. The only "warehouse" I know of is in NY although there are most likely others near factories, I've heard of a sale in Hauppauge b/c Estee Lauder has a factory there.
EDIT: I used the magical google. This turned up
on a site:
Closed Door Sale" at Estee Lauder Warehouse - July 23rd [2005, the last update of this page was 2005]
The Employee Activities Council has tickets for a "Closed Door" sale for invited guests at the Estee Lauder Warehouse at 90 Nicon Court, Hauppauge. There is no fee to attend this private sale. All Estee Lauder products are sold at discount prices and are not to be re-sold. Your neighbors and/or friends are invited. Please call Dorothy Kutzin at 632-6040 if you would like some tickets. There are many individual items as well as great gift sets.