Perhaps he is late for this answer but I had not entered this forum, if my memory serves me right one of publications where you can consult these values is "Manual Fluid-Flow" whose author is Crane, another publication is the "Cameron Hydraulic Data".
Other Standard that you can consult is the ASME 16.47, Large Diameter Steel Flanges - NPS 26 through NPS 60, but I don´t know which is the actual or last edition.