I too was/have been interested in the production of an NA manifold. Lots of people tried, and a lot of them saw very little gain. It was very sad.
However, the one manifold that seems to do something is the
JUN Auto GT Surge Tank. That price tag though. :p There was a guy on the forums with full bolt-ons NA, and then went ahead and threw this thing on and made another 12HP or something after a tune to account for the changes in airflow. Tempting, but that cost is unjustifiable unless you're just itching like mad. There's a post on here about it somewhere.