Primary candidates are Perixx' keyboards (335BR is the mechanical contender, but they have a bunch of cheap membrane Sculpt-likes), Logitech K860 (if you're OK with a full-sized keyboard, it's pretty solid), or one of a few two-part options - I made a list when picking mine.
Wow, that's a great help! I love the look of the K860 - it's like a sculpt clone. I would buy one right away, but now you've gotten me interested in checking out all these others.... Is there somewhere I can try this stuff out?
Depends on where you are in the world - e.g. here in Ukraine you can occasionally see an ergonomic keyboard or two among the office keyboards in electronics stores.
From my own experience (having replaced my Sculpt with K860 when it came out) I'll say that it feels pretty similar, but keys take slightly less force to actuate. Supposedly Microsoft Surface Ergonomic Keyboard is also similar, but I haven't had a chance to try out that one.