Wow, are they Out of stock temporarily or permanently?
https://www.microsoftstore.com/store/msusa/en_US/pdp/Natural...
EDIT: They still offer plenty of Ergonomic keyboards, but only wireless one it seems. (For instance: https://www.microsoftstore.com/store/msusa/en_US/pdp/Wireles... )
Cheap MS Natural 4000: https://www.microsoft.com/accessories/en-us/products/keyboar... (rubber domes - actually I think the space bar is OK, but tends to be stiff until it's had a couple of weeks of use)
More expensive MS Sculpt Ergonomic: https://www.microsoft.com/accessories/en-us/products/keyboar... (scissor switches + clicky buttons for F keys and Esc)
Both are OK, I'd say. The 4000 has slightly nasty keyswitches, but in exchange it's got all the keys in traditional places. The Sculpt is nicer to type on, if you don't mind that sort of thing, but the non-standard keyboard layout leaves something to be desired.
(One note of caution: I've had 5 of the MS 4000s now, and the newest one, bought a month ago, has a much squishier, quieter key action - presumably a new recipe with improved cost-effectiveness. I don't think this is any worse than what was there already, but some might disagree...)
It looks like Microsoft brought this back as a new model in black with fake chrome, unlike the old beige model. (Still has the crappy spacebar mechanism, though; the spacebar is huge but has to be pushed near its center.)