Ladan,
You don't use cap rates, but you have the right line of thought in that companies are valued as a series of future cash flows.
There are any number of websites that list companies for sale just like homes or anything else. There are also business brokers. The guys I know that do this frequently tend to find out about them through attorneys and accountants.
As for values, those can vary for any number of reasons. While most companies are valued off of an EBITDA multiple, you have to take other factors into account: what if the company owns prime real estate, what if the company has a pending lawsuit, etc.