michswiss, I guess you are from CH? Have you checked SSR Reisen? (www.ssr.ch)
They have fares for ZRHAKL ranging from 5,090CHF (Garuda) and 5,600CHF (BA/QF). And inbetween are KE and TG. All business class fares.
If these KE and TG fares allow for stopovers at their respective hub cities, then adding a 'sidetrip' from SEL to NRT or even from BKK to NRT would not be that bad.
Yes, RTW tickets often have advanced purchase requirements.