Looking at doing a clutch cable swap for first time on Derbi cross city any simple step by step instructions as nothing on YouTube

If you can get it out of the tank, buy a blank of the same, clamp them together & gently file the new key.

Not sure how much this will help...but....if you can't get a hold of a Derbi dealership (I'm pretty sure that Derbi is owned by Piagio now,) You might be able to go to a piagio or vespa dealership...once again if no luck, usually a good cable will run you about $30.00. Any bike shop that does moto cross stuff should be able to custom make one...(they use special solder for the ends) and usually not for a lot of money either....30.00-50.00.
hope it helps...Cafemoto