Dark Eldar Attack in Space Crusade.

TLDR: You can replace a Marine Squad in Space Crusade with Dark Eldar Kabalite Warriors. They do drugs and soul stealing.
You can buy a box with 10 Dark Eldar, you get the weapons shown above.

Now you can use the Dark Eldar as Eldar, and then the Sybarite is an Exarch. You can get the "Eldar Attack" Card images online, the Dark Lance is a Las-Cannon and so on. Job done.

But, if you want them to be Dark Eldar, they don't have psychic powers, so they are more like Space Marines. But we have to make them different.

Dark Eldar Flavor:
  • Combat Drugs
  • Power From Pain
  • Fast Movers
A simple thing to do is to make them Space Marines, but the Sybarite has only 4 health points and you have no weapon upgrade cards, just the order cards. To compensate, you get drug tokens, 2 per miniature at the start of the game. Speed is 8, 4 for heavy weapons, 5 man squad.  You get a drug token if you are within 1 square of a living non- Dark Eldar when they die. Androids aren't living. This is "Power from Pain", the drug tokens are actually pain/drug tokens.
Any Dark Eldar miniature may use 1 drug token per turn, the token is placed at the end of the turn and activated at the start of the next turn, when you chose its one-time effect on a single miniature:

Drug Tokens:
  1. Speed: +3 Squares
  2. Strength: One reroll in Close Combat, Attack or Defense
  3. Accuracy: One reroll in Ranged Attack
  4. ZigZag: One reroll in defence vs Ranged Attack
  5. Awareness: Reveal all blips within 3 squares of the user.
  6. Move/Shoot/Move: Move part of you allowance, fire, and use the rest of your movement.
If the drug effect doesn't actually get used, then it was wasted.

The Shredder fires a net which slices up the target. I'll call it a Special Weapon, not a Heavy Weapon. It has an area effect (separate rolls for each miniature), it may permanently immobilize the target, and you move the full 8 squares. You can immobilize Dreadnoughts, then Move/Shoot/Move. The Dark Lance is a more focused Missile Launcher and the Splinter Cannon is a less focussed Assault Cannon. The Splinter Rifle is a bolter. The Disintegrator Cannon is a Plasma Rifle.

If the Dark Eldar player can corner some enemy and use up a couple of drug tokens to kill them all, they should get the tokens back from eating their souls. So the Dark Eldar ride a wave of violent death, eliminating strong enemies "Just as Planned". Their weapons aren't as good as Space Marines, so you can easily get wiped out if you get off to a bad start.
The drugs and lust for killing are a good contrast to the holier-than-thou Space Marines.

Alternative version:
Dark Eldar, set up as Blood Angels or Ultramarines. The Sybarite Commander has only 4 health points.  Lose 1 Equipment Card, gain a "Combat Drugs" Order Card. For the rest of the turn the Combat Drugs card gives all the Dark Eldar 2 extra movement square, and they may reroll 1 die from each of their attack rolls. If they kill 2 or more non-Android enemy (Power From Pain) in that turn, they get the Combat Drugs card back, otherwise not.

Other Races:
Feel free to make up a Tau Fire Warrior team with Gun Drones, Necrons, Cultists or whatever you have. Often there are old-style 40K miniatures on eBay that nobody wants, but just the thing for old school Space Crusade.