Coliseum : Mk4 enhanced performance core missing

I I'm llooking for Mk 4 enhanced performance core materials, to upgrade R5D4 and Zeb to level 85 and beyond.

I just beat tier 8 against the Krayt Dragon, but the last crate des not grant those materials. Nor any of the next crate up to 50% of tier 9.

Where can I get thèse materials without crédit card ? I spent 6000 or 7300 cristal for each of the 4released  characters and have all of them at 5. stars. 

I was expecting to level up my characters at least to gear XIII (level 115), including Rotta.