This is what I found about the 2006 DVD's going out of print from savestarwars.com
September 11th, 2011: 2006 DVD Conatining Original Theatrical Versions Now Out of Print
According to retailers, the 2006 DVDs of the original trilogy, which contained a second bonus disc for each film featuring the original theatrical versions, are no longer being manufactured. Amazon lists it as out-of-print, and no new shipments have been received by retailers for some time now, which has led to their rapidly dwindling numbers in stores. Chances are if you go to your big chain store like Target, Best Buy, Wal-Mart and the like, you won't be able to find them.
This means that it is no longer possible to officially purchase in any format, in any quality, the original versions of the films. The 2006 2-disc DVD sets were always marked as "Limited Edition", but now that has become true in the very real sense of the word. In short, the one thing the original versions clung to life on is now gone.
According to an employee at Barnes and Nobles, they were told by the manufacturer that it had gone out of print in April of this year--just when Blu-ray pre-orders went live. Coincidence? I think not. Lucasfilm deliberately orchestrated this in advance so that those people who are now rejecting the Blu-ray have no alternative. The Special Edition will be the only version offered.
As it happens, those 2-disc 2006 editions were the only original trilogy DVDs being sold, period; the "trilogy packs" you saw on sale contained those editions. Those trilogy packs are also now out of print. This means the 2004 Special Edition is also no longer available now--nor is any DVD version of any version of the film. In a calculated move, Lucasfilm has made it impossible to officially buy anything other than the 2011 Blu-ray. Sneaky buggers.
Of course, the DVDs thrive in second hand stores, used online retailers and e-bay. If you want any of these, better get them now! Even though the release was very heavily criticized because of the poor treatment of the originals (see here to find out why), it is very sad to see them fade away if only because of the symbolic victory of having the original versions technically available to consumers.