Magic items/weapons that level with character

[SolarSystem]

I remember encountering rules for this at some point in the past.
Does anyone have a source for where to find rules for this concept?

Will be playing Pathfinder, but any compatible source will do.

[Big Fau]

Weapons of Legacy, Item familiars (SRD), and a couple of others are the common ones. Pathfinder may have other rules.

[Extra Anchovies]

Pathfinder may have other rules.

It does! Scaling Magic Items (http://www.d20pfsrd.com/gamemastering/other-rules/scaling-magic-items), from Pathfinder Unchained.

[Bohandas]

There's also the Soulknife psionoc class and a couple of PRCs in BoVD and BoED

[SolarSystem]

Thank you all. Scaling magic items seems closest to what I had in mind.

[Shalist]

Possibly worth mentioning is Enhance Item (EHB pg 114), a non-epic feat that lets you use your key ability score for creating magic items rather than the minimum possible to determine item DCs; i.e. a 24 intelligence fireball wand's DC would be (10 + 3 + 7) 20 instead of (10 + 3 + 1) 14.

It applies to a single item creation feat, but if you use it on (for instance) an Eberron cost reducer feat, it'd apply to everything you craft.

[Calthropstu]

There is also a mythic ability you can invest in that will make an item legendary that will scale as you invest more mythic traits in it.

There is also the black blade.

[Bohandas]

Weapons with the Psychic ability scale to current power points (which is affected by max power points, which scales to manifester level)

[Gruftzwerg]

would kensai (prc) be an option? you could have your own signature weapon which will level as you increase in the prc and imbue it with more magic/rituals.