This is a fascinating question that I've been obsessing over for a while as well. A friend and I even talked of creating a small market-sizing app to address this question, among others, but we haven't found time to work on it.

Every approach I can think of for the general question seems to involve tedious, brute force attacks like tracking down every incorporated business and looking up their catalog and calling them about recent launches. And that doesn't even get at unincorporated businesses.

You also have to define what you mean by "new product." Is a restaurant trying a new special launching a new product? Are things produced by major software platforms products or features? Are things made by really small startups features rather than products?

I can think of a dozen approximation techniques that would generate decent upper or lower bound estimates that might work for specific applications, but none that would solve the problem rigorously for all problems. I don't know of any analyst firm that works on this either.

If I had to take a quick first stab at the organized part of the market, I'd look at UPC stats. These won't cover everything, but you can use them as a basis from which to estimate other categories like informal, SaaS software etc.
http://en.wikipedia.org/wiki/Uni...