Making real balsamic vinegar is a tightly held secret by the makers. I have looked for this as well and while I have been able to find out a lot of the process, there are key questions that go unanswered. They have to do with how you manage to keep the vinegar going and fermenting for 12 years and more without it turning to water (as usually happens in a few months with regular vinegar)? How long exactly you keep it in each kind of barrel in that 12 year or longer period? What exactly are the temperature fluctuations that are needed?

I think you pretty much have to know someone. There is a guy in Napa who is going at it. You might try getting in touch with him. See this link.

http://www.youtube.com/watch?v=cKkc_VwBcrw