Neither a cockpit or an S-duct are known to be out there, at least to me (and I’ve been keeping an eye out for both for 20 years or so). Overall I have seen very, very few aftermarket items for the 1:100 scale kits, and almost all of those have been decal sheets.
1:100 is such an oddball scale, which is a shame because the Nitto/Doyusha TriStar and 707 are two of the best-looking airliner kits I’ve ever seen.
Jodie Peeler
"In any dispute the intensity of feeling is inversely proportional to the value of the issues at stake." - Sayre's Law