I've been working with these folks in Germany and they are available for all three Derbi engine types. Yup they are expensive. I am running the prototype on my daughter-in-law's pyramid reed Variant that I converted to 12V with batteries. I modified a DS-50 starter for it and she finally stopped whining. I have never had any Derbi idle or rev this well since it has such great spark now. Bite the bullet and get one! I am also building a "barn find" Sport Laguna (Laguna TS) into a European "Coppa" by dropping the fairing AND the clamp on bars, using the earlier Variant handlebars plus an NOS Rinder #335 headlight. This will get a Powerdynamo system also!
Here's the new direct Powerdynamo link. 1977 Mopeds and Treatland should be carrying them if you bug them enough.
I would order them through our "dealers", however, because they get a better price for us than directly ordering them through PowerDynamo.