Any way to get More Sneak Attack dices? As in with feats, or variants

[Leathros]

I'm playing a Trickster Spellthief, and I already made my mind about it, and find it more useful to have a spellcasting progression, but I want to have at least 2d6 sneak attack dices, so I can steal 2 spells with only 1 attack. Is there a way to get more SA dices without spending lvls on it?

[Doctor Awkward]

-Rogue's Vest from Dungeon Master's Guide II grants +1d6 sneak attack.
-Precision Weapon enhancement from MIC grants +1d6 sneak attack to attacks made with that weapon.
-For two feats you can pick up a Shadow Blade maneuver and then Assassin's Stance from Tome of Battle. You get +2d6 sneak attack when you are in that stance.
-The spell Nightstalker's Transformation from Spell Compendium arguably grants you 3d6 sneak attack, but it has wonky wording on whether or not it stacks with other sources
-The spell Hunter's Eye from Player's Handbook II is a Ranger spell that grants you +1d6 sneak attack per three caster levels. It only lasts one round, but it's a level 1spell EDIT: Nope, sorry, it's level 2, so I think a permanent version that grants you +1d6 forever would be something like 16,000 gold?

[AnonymousPepper]

How many of those are just sneak attack and how many apply to precision damage in general?

Curious about how much of it would work with Swift Hunters.

[Darrin]

Martial Study + Martial Stance feats (Tome of Battle) will give you Assassin's Stance (+2d6 sneak attack) if your Initiator Level is high enough.

Dragonfire Strike (Dragon Magic) will give you +1d6 sneak attack, but will change all of it to [fire] damage.

Rogue's Vest also appears in the MIC and gives you +1d6 sneak attack. Cheaper, too. I'm not sure what you mean by the Precision weapon enhancement, but Precise doesn't do what you think it does. The Assassination property in the Cityscape Web Enhancement does give you +1d6 sneak attack.

Mantle of the Predator (8000 GP, MIC) gives you something that's mechanically equivalent to +1d6 sneak attack, but doesn't call it that for some reason.

Dipping into Sneak Attack Fighter, Unseen Seer, Spellthief, Ronin, or Nightsong Enforcer could get you additional sneak attack dice.

[Doctor Awkward]

I'm not sure what you mean by the Precision weapon enhancement, but Precise doesn't do what you think it does.

Deadly Precision weapon property, MIC pg. 32.
+1d6 damage when sneak attacking or sudden striking. +1 enhancement.

[Darrin]

Deadly Precision weapon property, MIC pg. 32.
+1d6 damage when sneak attacking or sudden striking. +1 enhancement.

Aha. I thought there was something else in the MIC... so Deadly Precision + Assassination property = +2d6 sneak attack.

There's also a feat called Deadly Precision in the XPH, but the Bracers of Murder(8000 GP, Drow of the Underdark) are even better: reroll all 1's, and you can keep rolling until they aren't 1's anymore.

[Segev]

If you've got sor/wiz spells in your possible spells to cast, Heroics is a spell from the spell compendium. Level 2, it gives you a fighter bonus feat for 10 min/level. Cast it twice and have an IL of 5 (requiring level 10 if you've no levels as an initiator), and you can pick up Martial Study and Martial Stance for the requisite maneuver and Assassin's Stance, spending nothing but two 2nd level spell slots.

[deuxhero]

While not extra die (though this means it's multiplied on a crit), the Craven feat (champions of ruin) give an extra point of damage per level when making a sneak attack

[Calimehter]

Since you have caster levels, there is also the Razing Strike feat from CAdv. Its pretty situational, but it applies to constructs, which are normally immune to your SA. See if your DM would allow sacrificing a stolen/borrowed divine spell to expand the feat's use to undead.

[Troacctid]

Halfling Rogue substitution level from Races of the Wild gives you +1d6 sneak attack with thrown weapons and slings and -1d6 with melee weapons.

[Waddacku]

I find the idea that you can give up 1d6 multiple times on one attack to steal more spells questionable.

[Jowgen]

Since you're already using dragon mag, Dragon 318 p. 54 has the Mutineer's eye graft, which gives an extra d6 for 4000 gp.

[Doctor Awkward]

How many of those are just sneak attack and how many apply to precision damage in general?

Curious about how much of it would work with Swift Hunters.

The updated Rogue's Vest in MIC does.

There is almost no support for skirmish outside of a few very specific items (scout's headband, gloves of agile striking, skirmisher boots) and the feats in Complete Adventurer and Complete Scoundrel.

It's a very common house-rule at my group's table that most things that benefit Sneak Attack, especially if they also call out Sudden Strike, simply say "precision damage" and thus also affect Skirmish accordingly.

[Jack_Simth]

Dipping into Sneak Attack Fighter, Unseen Seer, Spellthief, Ronin, or Nightsong Enforcer could get you additional sneak attack dice.

(Emphasis added)

Hard to dip into one's primary class. The OP is already playing a Spellthief - not that it matters, as the OP doesn't want to expend levels on it. I considered suggesting Unseen Seer or Arcane Trickster myself - however, spell levels stolen are tied to class levels for the Spellthief. To an extent, that can be fixed via the Master Spellthief feat (Complete Scoundrel) but the OP would still be missing out on a lot of useful stuff from the class.