Originally Posted by ISTFlyer

OK, in this case, all flights need to have individual "I" fare availability as well. For example, if you are planning to book MXP-ZRH-LAX; you would also need to search MXP-ZRH and ZRH-LAX separately and search for "I" fare availability for each of those segments.

Booking married segment availability on TK Miles&Smiles is not possible.



Exactly, it's a known issue that not all bookable combinations show up on TK.com
If there is "I" fare and the flights doesn't show up online; the best way is to either call in or contact a sales office.

Visiting a sales office in person would increase the chances for you to book a ticket.