You cannot get promo colors on wearables, as a general rule. I have asked this specific question - just a couple of months ago - because we wanted a Flint's sheath but wondered what other options there would be to order colors.

I was told that they cannot do custom pours of promo colorations, but that I could get a wearable of one type in the signature of another wearable. So, we were thinking Ika's Sheath signature glowing color on a Flint sheath and they said that was possible.

If you want something that isn't available on Flint's sheath or another wearable, the best bet is to comb the Clearance regularly and try to catch one. But after trying that, it's very hard to do - I managed to get one on the BF sale that looked like a glittery Jupiter coloration, but that was sheer luck.