You could take it to a rock shop, they should have a machine to cut the core, and be able to cut it in under 20 minutes.
I have a large ferrite C core.
I need to get it cut, once I do I may have a few extra sets.
I don't think it's the right core material though...It's ferrite, 2000 permeability which is too high....Same material Tony Woodside has and he's getting resonance but no gas production.....Which seems to be a common theme.
If anyone has ferrite and does no know how to cut it you need a diamond blade and a lot of water!
Unfortunately I don't have a saw so I was thinking about taking it to a machine shop?