What scale? The free "Brigand caves" supplement for Stonehell is a big cave lair with like 20 bandits which I got a lot of use out of. ACKS Lairs & Encounters has a simple 200 brigand lair which is more like a Roman army camp (and like 100 other lairs).
Although the total force is 99 (80 0-level bandits, with 19 guards/leaders = 99 total combatants), so a bit larger than what you're initially looking for.
I have an NPC party of bandits in a river crossing using tropes from The Good, The Bad and The Ugly...but it's fairly high-level (6-8th) and AD&D specific. PM me Maynard if you have an interest.
I don't have a bandit lair but I have a free booklet on bandit NPCs that talks a little about the culture of rural criminals. Wrote it up to be compatible with Swords & Wizardry and my Majestic Fantasy RPG.