I needed a core so I saved a paper towel core from the trash bin. I "varnished" it with some nitrocellulose based nail polish overcoat. Then gave it 3 or 4 spiral wraps with scotch tape.
I did a new board Mr Dave style today.
The plan I'm forming is to use the left one with a coil like the one I wound last night and the right one selects a band by selecting a fixed capacitor.
Then use a small variable cap for the band spread.