Yeah, thunderstones. You could, optionally, have archers with thunderstones instead of arrowheads, putting a -2 to the attack roll (maybe more?) and a similar deduction to damage, plus the thunderstone's sonic boom thing.

I mean, alchemy is a skill, with nothing to do necessarily with magic. In a low magic world, it would make sense that people would be progressing towards science and alchemy to make up the gap. So make the most of alchemy. Thunderstones work, and I believe that there's some more alchemical items in the Complete books, Scoundrel and Adventurer particularly. Also, I think somewhere there's a list of alchemical items used by ninjas, some of which would have to be useful. Perhaps also check some of Monte's Malhavoc stuff, definitely Arcana Unearthed and maybe Iron Heroes.

I'd give you more useful info, but I'm at work, away from books. I'll check later, though.

And I just got CS! I'll have to check out the reqs at home--was it +2d6 or less?

strong sleep poison... then gags, blindfolds and restraints (or what I call a fun Saturday night... ba dump bump).

Seriously though; if they're going after known spellcasters in a relatively magic poor world, they would use mundane methods at their disposal to catch them... so rogues dealing nonleathal sneak attack damage or trying to knock them out and 'capture' them.

good luck...

;o)
Dan

Monks. They can deal non-lethal damage without penalty, have the best saves, evasion (since the party is 4th level).

Once someone is pinned you can, at your option, prevent them from speaking.

Round one, tanglefoot bags and thunderstones.
Round two, initiate grapples
Round three, monks twist wizard into a bitch-pretzel.

Steal spell component pouch.
Grapple and pin.
Monks with stunning fist.

4th level sorcerer? I don't think they need any help in killing him, spellcasters are dramatically weaker at lower levels. A rogue is easily enough to take out such a character. Just try to have the enemy group have the element of surprise.

If you want it to be a unique experience, use unique tactics - but there really isn't a need to go spellcaster-specific at that low of a level. Bolas work effectively against fighter and caster alike, as do surprise rounds and sleep spells.

If you really want to be a bastard you can throw in an Occult Slayer :D they seem to do the job quite nicely.