Warehouse 23 has them back in-stock for a very limited time. It's not the full line, and the prices are higher than they used to be, but if you have any holes in your collection and want to fill them with metal, now's the time to do it because apparently once they run through what they have up on the site, that's it, and they'll be taken off of W23 on April 11. After that, you'll need to hit eBay.
Still, if you need to have that Doppelsoldner or a MK-VI Ogre, and aren't afraid of a slightly hefty price, act now or hold your peace for a long time.
The announcement said the pre-orders weren't starting until Monday April 7, but I see them up on the site now and apparently you can put them in your cart (I haven't tried to complete an order yet), so it could be a mistake that they're visible now, but give it a try.
EDIT: Now with the correct link!