[2019] Sweet dreams - what’s the best way to get it?

Like most people Ive got a few hundred hours into the game now, and not had a sniff of this exotic

Ive ran Potomac event centre on challenging countless times
Ive ran Roosevelt island on challenging countless times
Ive completed countless Outcast bounties

Either Im doing something wrong, or RNGesus hates me.

Is there a tried and tested method of getting it?