Most US electric power utilities are EPRI members. If you know anyone in the main office of a US power utility, you can ask them to look up some specific information for you, but it is not permitted to copy or distribute these reports.
The Once thru unit water treatment guidelines are also published in europe by the VGB and also the german boiler code TRD. These are a lower cost publication compared to the Epri guidelines, and are probably more reliable.
You can also try a science citation abstract search of the usual authors ( Barry Dooley, Otakar Jones, etc.)