So close

Pretty sure they were rewards from the marquee event. I have enough of them to go past that level, but the next one up (Masterwork Performance Core) doesn't seem available anywhere unless you pay.

Although, when I searched for it, I found it was available in the Sergeant Melshi and Bail Organa marquee events running in 62 days and 76 days respectively!

I just checked and it's the same for me.  I guess we earned them on lower tiers of the coliseum.

No I can’t even buy em lol I’ve looked where I can get them, and it’s only showing the next marquees. 

There's always a way.  Your bank manager may not like it, but there's away $_$