Horrible the farm of the collection of the new event, it is always the same ones which fall and sometimes, the same one just after...
All collections are always RNG, you have to either keep running or buy what you need on the broker - the system isn't any different from any other time, other than the fact they're not all in the event instance. But then again other events aren't always either. Sounds like you're just having a bit of a bad RNGesus experience.
Which ones? There is 6 in the open world, and 2 in the alert. The other 3 you have to get from outside the event content.