Heater cables use an outer sheath available in any length at at most good cycle shops. The inner "wire" is not a cable but a single wire, this is usually piano wire available from most model shops in 1 metre lengths (enough for a Libra), used for servos & point motors which require a push pull action, as on the GTM Libra. We made our own heater controls with inner/outer as described above.
www.gtmoc.co.uk also now known as
www.dadbarry70.co.uk.