Not that I can find. Keyboards are so cheap these days that surely it doesn't matter? was this a particularly expensive keyboard? I guess you could measure the dimensions of the missing key, then buy a dirt cheap keyboard (as cheap as you can find) with the spacebar key of the same dimensions
But that's the complex and unnecessary solution.
- you would look a bit strange going round a store with measuring tape
Have you tried bribery with the 4 year old? If it didn't work, and she truly has forgotten where she put it, maybe look for it?
I'm sorry, but in this day and age it's probably less expensive to just buy a new keyboard rather than scour ebay for a spacebar, then pay 10 on the shipping =/
=EDIT=
Unless this is a
laptop keyboard you're talking about? Contact the manufacturer, produce whatever alibi you like, but don't ask me, I can't help you with anything "illegal"