Matt has, I think, the right idea indeed!
CyberHobby "specializes" in one-offs and odd things - consider of course that Pz II C with mine-rollers they just recently put out, or the upcoming 37mm Flak 37 auf Opel Maultier, or the upcoming Flak 43 turm auf Pz. III, or that SdKfz 250 w/ 5cm PaK 38 - which likely wasn't even really a German creation at all! CH is definitely into one-offs and odd stuff! Yeah, Meng, or, for that matter, Hobby Boss, Bronco, etc., too! But my money would be more on the D and his specialist child, CH.
IMHO, CH would be the best likely for this one - as they already have all the actual Pz. III tracks, road-gear, etc. which show up on this, and those are key steps up on any other company trying to pick this monster for developing a kit of!
Be that as it may, I would LOVE to have a good styrene kit of this and would really LOVE to add this to my cabinet of small military curiosities!
Bob