How to build a network for Investor-Operator networks?

Venture Firms are famously known for having highly exclusive networks of their own and that is part of their identity(brand). It takes years to build that network, and most are not willing to share their connections publicly. Visible Connect[1] and Angel List seems to be building such a platform for angels and venture firms. How would you get around getting these kind of customers without a network in VC? Why isn't there a global scale network for Venture Firms or a YC for multiple Firms? [1] https://connect.visible.vc/