Murata has the curves, too, but they're stingy with them. They also have "powdered metal" "ferrites" that have much flatter saturation curves (like the powdered metal inductors but lossy like a ferrite bead).
Just use a second one of the one that you are measuring.
I do that to measure the nonlinearity of ceramic caps. Measure capacitance of two in series and tweak the bias at midpoint.
-- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
This site has some nice scope traces (scroll down):
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