COSMIC was recently updated (Whole Genomes v78, released 05-SEP-16). You need to make sure that you use correct gene identifier for your search. 

You can also try ICGC Data Portal: https://dcc.icgc.org/

or DoCM: http://docm.genome.wustl.edu/

you can use http://www.tumorportal.org/

super easy to use!

good luck

Dear Valentine Comaills, dear Roman Mezencev,

Thanks a lot for your answers, they were helpful!

All the best,

Jasmine