Capital markets for pref

Hey all - I'm seeking to better understand the capital markets for preferred equity, both for search-type deals as well as for real estate deals. My understanding today is that there are pretty mature markets for debt, but that pref is often done in secret.

Do any on here have good intermediaries for pref that you're willing to share? Might it be a product opportunity to create such a platform (Possibly under Reg-A, Reg-D, or Reg-CF)?