I saw few sellers from Zgorzelec/Gorlitz (border City between Czech, Germany and Poland) with ridiculous large quantities available, highly likely they get their sets from Kladno as well as WH in Germany.
I Know "Kladno capabilities" .. trust me, its virtually just next door. Its impossible that they would get it somehow "officially" (i mean truck loads). Each employee is awarded among other incentives a certain (limited) discount that entitles him to buy .. umm. let say 10-20 average sets (1000-2000 pcs) per year at half a price. You cant steal anything from the factory - not even a single brick that fell on a floor hardly an entire box.. so they have to have their source elsewhere.. I have come across truly disturbing facts that while the ppl in the Kladno factory itself are guarded like prisoners (more or less), the 3rd party Logistics partner with warehouse in other part of "greater Prague" obviously not.. and that might be where they could be getting their loot from.. I mean.. if an avg employee buys something at 50 % of local RRP, he certainly doesnt sell it to you at the same price - where would be the profit?
now these Logistics ppl.. if they are willing to sell the same set for 35 % of the local RRP.. I think everybody comes to the specific and exact explanation how did they land their hands onto it..