Where Can I buy Transformer Core Ferrites for Frequencies ABOVE 200 MHz ?

I know of 200 MHz ferrites e.g. by National Magnetics Group. Are there any ferrites good for transformers above 200 MHz?

Supposedly Hexaferrite (barium ferrite) works at such frequencies. But I have found information that it has permeability = 1.1, so it is not much gently speaking. If there are such high-frequency ferrites with decent permeabilities, where can I buy them?

i bet there are tons of companies over the world selling your devices, for ex: here is the link
https://www.mag-inc.com/Products/Fer...-Ferrite-Cores
here also provides you helpful extent about magnetic materials that are able to answer the second question as well
hope it helps,
TM

Seems they aren't economical to mass produce otherwise they would likely be found in all the major cellphones, laptops and other devices which make use of wifi and similar RF bands. Log periodics seem the simplest way to broadband reception.