it's not that simple, I've looked into it, the packaging will be hard.
first, I can't find any keyboards that are just the right size. either they're miniscule, or netbook sized, not palmtop sized. Also a lot of them are bluetooth with no USB connection so you'd have to do a bunch of stuff to wire it properly.
so it seems to me that at least for the keyboard you'd have to do it yourself, this shouldn't be terribly hard if you can use some perfboard or something. They have tutorials online to wire up a matrix keyboard so it's doable, you would have to source push buttons and we would have to find out what kind make the best keys for typing on.
if you're at 10" that's already a netbook size anyway so I wouldn't really call it a handheld.
IMO if you could make a PC110 clone with newer hardware it would be just about perfect.
one thing that sucks is all the small screens are lame 16:9 bullshit.
I think making one is doable but it will take a lot of design, I don't think it's easy to throw together, at least not anything that will look and feel good.