I don't know such a source but you may be able to find some after some research. Like Spree is an open source product but the company behind it employs developers to work on the product.
I really wish someone would do a PhD dissertation on it, or write a book on it, or something. I guess it's likely that there's something somewhat like what I'm looking for out there already.
Clearly there is a massive open source economy. I would like to understand that better.