The internal teleflex cable core was provided in bulk to those that provided specialty speedo and tachometer services. The one end could be formed in a special machine like a spot welder to provide a square end and the other end generally has some form of swaged on drive end. I've seen universal cables that have a measure of bulk cable core and a swage on fitting with a tool to swage it for the DIY guys. Now whether you can get a long enough core or the correct swage this way, I don't know.
There is only one place that performs this service in San Antonio at a shop called S.X. Callahan, Inc and caters to the trucking and industrial community here. I'm not certain that they are still in business but they may still be.
A link to Bratton's:
https://www.brattons.com/28-m30-113-...er-cables.html