It would be nice to keep a little bean on my desk, cannot find one anywhere.
Posters, calendars, screen savers, yes. Architectural models, paper weights, no dice.
Is there a reason for this?
That’s the silvery blob thingie we saw in “Source Code”, right? 
Yep
You’ve found a nickname for Cloud Gate that would irritate Kapoor even more than The Bean.
Yes, a sculptural representation would infringe the artist’s copyright in the sculpture. A two-dimensional photographic or artistic representation does not, by the terms of US statute.
Interestingly, some of the major donors to Millennium Park did get maquettes. I was touring a private art collection last year and asked the homeowner about his. “Oh, that’s the most expensive piece in the entire house,” he said with a wink.