Are these powerline (50/60 Hz) Hz?
If so, if you know a transformer manufacturer, they can custom-make some for you. Emphasis on custom.
Essentially, instead of interleaving the E and I laminations, you form a stack with only "E"s on one side and the "I"s on the other.
Then empirically start adding nonmagnetic spacers to create an air gap between them. That air gap will be very small 3 mm or less. Usually you may require of kapton film layers.
Once that you have achieved the desired inductance, set the gap with hard epoxy.
The resulting assembly will be VERY NOISY. You'll have to pot the complete assembly in a can filled with tar-pitch. Similar to what magnetic ballasts employ.