extra d6 sneak attack damage

[NIghtrider]

Is there any way to add to your sneak attack dice (ie a 3rd level rogue doing more than 2d6 for example). Are there any items that add to it. If not, what would it cost?

[Darigaaz the Igniter]

Only thing that comes to mind off the top of my head is the Precise Strike teamwork feat. However, that's specifically an extra 1d6 of precision damage, and not 'increasing your sneak attack damage'.

[Raisse]

Look at the Sap Adept and Sap Master feats.

[RumpinRufus]

Well, it would be reasonable to houserule it as a +1 weapon enchantment. Compared to enchantments like Flaming or Shock, it has some disadvantages (have to be in flanking, some monsters are immune to precision damage) but it also has some advantages (because it can be used with many feats and abilities like Deadly Sneak or Harrow Strike.)

[Duiker]

If this was for a home game, I'd probably price it like the cleric's Phylactory of Positive Channeling, since their channeling advances at almost exactly the same manner as a rogue's sneak attack (1d6 every two levels): 11,000 adds 2d6. Refluff it as goggles of some kind since it's a headslot? Or change the slot to be gloves of some kind, that might be a better thematic fit.

Also, since clerics can channel only a limited amount per day, I'd consider either making it a limited use item (maybe 3+Dex bonus per day) or tack 50% onto the price, but really only if the rogue in question was getting to use it an abusive amount.

[strayshift]

Catfolk Rogues can take a Rogue Trick that gives their claw attacks d8 sneak attacks. At low levels this is pretty good, the only downside being the need to get an Amulet of Mighty Fists to boost them at higher levels.

A Ratfolk rogue can also have two claw attacks and a secondary 'tailblade' attack (so three attacks in all).

[Paulicus]

Knifemaster rogue uses d8s with knives/daggers.