Add marking to a power ...

[testsubject27]

I need to add the ability to mark a target to a melee power that doesn't have it by virtue of power and class. Is there a feat or paragon path or magical item even that does this?

And I am a tiefling, not a halfelf.

[allonym]

A few things off the top of my head (definitely not exhaustive):
If it's a divine power, the Cleric paragon path Tactical Warpriest can add a mark with bona fide mark punishment to it.
If it's a rattling attack (or you can make it rattling) you can add a mark with the Strong Arm Enforcer rogue paragon path.
There are a few multiclass feats which give you a mark.

Could you provide more context?

[Epinephrine]

If it's an arcane power, you could use a weapon of arcane bonds (encounter power, save ends).

[allonym]

There's also the Predatory Weapon, which gives you an encounter power which lets you mark a target within 5 of you when you hit. There's nothing stopping the mark affect the same target you just hit.

Edit: And the Blade Bravo rogue paragon path, which adds a mark to every single one of your melee attacks if they grant CA.