Negative energy damage to manufactured weapons, unarmed strikes, or natural weapons?

[Genesist]

I'm making a build in which I am looking for a way to add negative energy damage to attacks on a consistent basis. This rules out adding it from a spell that lasts one attack, or through some manipulation of negative energy channel.

Is there any unique item, item quality, class feature, feat, etc. that would allow me to consistently add any amount of negative energy to my attacks?

Alternatively, other than Lesser and Greater spirit totem, are there any other methods to gain consistent negative energy damage without adding it to attacks. Bonus if it's AOE like Greater spirit totem.

[Kazaan]

A Vicious enhancement on a weapon will cause it to deal 2d6 negative energy damage to the target and backlash 1d6 to the user.

[Wyrmholez]

Kazaan wrote:

A Vicious enhancement on a weapon will cause it to deal 2d6 negative energy damage to the target and backlash 1d6 to the user.

Vicious Damage is untyped. Although I can see why you say that, Enervation is a requirement to make it.

If vicious did negative energy Undead would be kind of scary.