One of those nice ceramic or equivalent coil formers with moulded-in
cut-outs for each turn of wire.

This is for a HF PA coil.

Ideally larger OD than 70mm and longer than13cm.

I'm unable to wind a large enough inductor on the one I have here
(65mm x 13cm).

It can only hold 26 turns with roughly 1-turn spacing.

Dig through your junk boxes please.
--
Philip de Cadenet G4ZOW
Transmitters 'R' Us
http://www.transmittersrus.com