Check this paper by Jerbi-Alon 2014, where they developed DAISY, a method to predict synthetic lethal pairs:
Jerby-Arnon L, Pfetzer N, Waldman YY, McGarry L, James D, Shanks E, Seashore-Ludlow B, Weinstock A, Geiger T, Clemons PA, Gottlieb E, Ruppin E. Predicting cancer-specific vulnerability via data-driven detection of synthetic lethality. Cell. 2014
They released a Cytoscape session file, containing all the synthetic lethal pairs synthetic dosage lethal pairs predicted.
In alternative you can contact the company Mission Therapeutics, which focuses on identifying new drug targets using synthetic lethality. I doubt they will release their data publicly, but depending on what you need you may propose them a collaboration or something like that.