You can download following Core Loss Files free. Each Core Loss File (in excel) contains the digital data on core loss data (core loss vs. flux density) at a specific frequency. Some may contains several core loss curves at upto 5 frequencies.
Electrical Steel NGO – AK Steel’s M-19
Electrical Steel GO – ATI’s M-6
Cobalt Steel – Carpenter’s 50A
Nickel Steel – Carpenter’s 49 NGO
Iron Powder Core – Micrometals -30 material
Alloy Powder Core – Magnetics’ KoolMu 40mu