Knowing the frequency will make it easier to guess the AL. You wont be very wrong if you get similar size core that is made for power transformers, most materials are about the same.
There are hundreds on offer by manufacturers but off the shelf the choice is limited to one or two.Au contaire, @vbase each supplier has at least a dozen types out of a thousand different mixes of ferrite.
for example TDK have hundreds from which dozens are most popular, like N87 or N30 or T65 or ...
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