Various sources give different information regarding permittivity of ferrites.
They seem to agree that epsr = 10 to 20 for NiZn ferrites, but for MnZn ferrites they quote values from 10 to 300.
I would like to know velocity of EM waves in ferrites, so knowing epsr would help.
It may be that the manufacturers do not know exactly - it will vary with temp, as many ferrites are quite conductive the permittivity would be ... very low as the dielectric constant is nearly infinite ... ?
You have to expect strong frequency dependence of permittivity and resistivity. A detailed discussion can be found in Snelling Soft Ferrites. See below curves for two NiZn ferrites.