Welcome to Librarium Online!
Just looking at the Dark Eldar Scourge set, whilst the Codex states they have splinter rifles and up to 4 can be upgraded to heavier weapons (2 DL,2 SC) are there actually any models with Scourges with Rifles available?
I can't see any on the GW website,as the boxset has the heavy weapons and syrabite?
From the looks of it, not anymore.
Hopefully this will be a non issue in about a month and a half, but until then you'll have to get splinter rifle scourges from other sources.