The only "official" places to buy authentic, new Lululemon is from their website, their own branded retail shops, or at gyms/fitness centers that are part of LL's partner program (see
Link hidden: Login to view.) Any that you see outside of these channels are used or liquidation items (bear in mind that an unworn item with the tag still attached is "new" by eBay standards but not "new" by retailer standards -- most returns even in pristine condition will end up on the liquidation heap.)
Because LL does end-of-season closeouts in their stores, I would hazard a guess that that is where a lot of these eBay suppliers who have hundreds of LL listings are getting their stuff.
Frank