I don't remember seeing a mod that does what you describe. But I do have a personal mod that started as a base for a larger mod that integrates some of the DLC weapons and armors into the Capital Wasteland. It doesn't cover everything however as there are items I felt were too unique to suddenly be found throughout the CW.
Here's what weapons and armors are covered:
Spoiler Added Tri-Beam Laser Rifles from Broken Steel into Brotherhood and Outcast leveled lists
Added Lever-Action Rifles from Point Lookout into Raider, Slaver, Talon, Super Mutant, loot and vendor lists
Added Double-Barrel Shotguns from Point Lookout into Raider, Slaver, Talon, Super Mutant, loot and vendor lists
Added Axe and Shovel from Point Lookout into Raider, loot and vendor lists
Added Infiltrators from The Pitt into Talon, Outcast, loot and vendor lists
Added Pitt Raider armors from The Pitt into Capital Wasteland Raider lists
Added Supervisor Helmet from The Pitt into Capital Wasteland Raider lists
I didn't bother with adding Tesla Cannons from Broken Steel. There's a perfectly fine mod, http://fallout3.nexusmods.com/downloads/file.php?id=7825 for that and it integrates Tesla Cannons in an immersive way.
While not a DLC weapon, Laser Rifles were added to Super Mutant Master's lists. I did this because regular Super Mutants and Brutes only get a couple of the DLC weapons and the Masters had nothing new. This also works like a step-up for SM's using energy weapons as Overlords use Tri-Beams yet no other SM's use energy weapons.
And I expanded the repair options for these weapons:
Spoiler Lever-Action Rifles can repair and be repaired by Hunting Rifles (Lincoln's Repeater is repaired by Hunting Rifles and it's a Lever-Action Rifle so...)
Double-Barrel Shotguns can repair and be repaired by Sawed-Off Shotguns (pretty self-explanatory)
Infiltrators can repair and be repaired by Assault Rifles (it is just a a different version of the Assault Rifle)
Tri-Beam Laser Rifles can repair and be repaired by Laser Rifles (you figure they would have mostly the same parts)
Pitt Raider armor can repair and be repaired by CW Raider armors
I could upload it if you're interested.