3-D printing is quite the up and coming thing at the moment – although smooth surfaces are still a bit of a problem. But you can buy some potentially useless items for your layout. How about N-gauge pigeons? They come in packs of 121 or 484. (Why 121? 11 x 11 on a sheet, I guess). Perhaps Duncan could add some to the Houses of Parliament, though these don’t look fat enough for a London pigeon living on a diet of ham sandwiches and crisps. See http://www.shapeways.com/model/499052/n-scale-1-160-pigeons-set-of-121.html
UPDATE – Only 3 pigeons were recorded on the Houses of Parliament…..