My sincere thanks for your interest / help on this. I did start by asking Herr Unger about these figures (including the Arquebusier mentioned by Tannenberg) but he told me he had no knowledge of the whereabouts of the moulds. He also suggested trying Scholz, since they seem(ed) to have the Neckel moulds ..........
But even with the engagement of Herr (Hans-G) Scholz himself it was not possible to take this any further at the time. Now that I see the Nf77 Dragoner Trompeter is indeed within one of the Scholz sets - thanks for your eagle eye Beloc - I'll try Herr Scholz again. [Edit: Scholz confirm they do not hold the Carabinier figure (Neckel Nf24), whether as part of a set or not.]
They are really nice figures, so I'll keep going and see if I can get them both.
[PS: Schmalkalder do indeed have the Arquebusier figure NRG13 and I have it on order along with some others.]