Furniture Sample-making  

prototypes
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Well, it all depends on what kind of prototype you want to make. What materials, etc. There are plenty of metal fabricators, and places that do custom upholstery in fabric and leather. There are wood-workers, carpenters and cabinet makers...
It's dificult to answer your question without knowing what you need to make.
Here, MDC does a lot of custom work. They could probably sub-contract anything they couldn't do in house. It's a start. http://www.mdcint.com/
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http://www.mdcint.com/

Sofas, tables, chairs...
A place for upholstered sofas;
Wooden chair;
tables;
Metal furniture;
Plastic, rotomoulded;
Generaly, fabricators that welcome custome made orders.
http://www.roumeliotisdesign.com