According to the German sl-club-pagode/Fahrzeuginfo website, for US-models the hazard warning flashers were standard as of 230SL 113.042.--.012498.
The German version received the flashers as standard equipment only with the 280SL 113.044.--.012089.
The flashers were available as a dealer installed option before, however.
My (280SL, production Oct.68, US model) flashers work without key and without engine running.
The hazard warning flasher wiring is included in the electric wiring diagram in the BBB, US version, as item 22 (page 15.54.82-0/7)
Klaus