Hey, just signed up finally. I've been playing the single player a fair bit and thought I had this same issue, thought I would post to help others hitting that breaking point of frustration. I went through many in-game days trying to find a Tundra Bandit lair for a quest given to me by the Vaegir Marshall, any time I just abandoned the quest to try and ask him for a different quest, he still had the same one for me. After much frustration I turned to cheats hoping to find it, searching with the 'Ctrl+T' cheat. I can confirm that using Ctrl+T
WILL NOT find it for you alone. What found it for me in the end was on the character page hitting Statistics, Exporting my Character. Alt-Tab, then find the Mount&Blade Warband Characters folder in My Documents and edit in notepad your character's Spotting and Tracking stats to 10 (Tracking may not be needed). Then import the saved changes and with the map revealed using Ctrl+T search thoroughly around areas central to that type of bandit as guided by the quest's on-pickup description, groups you can see with Ctrl+T etc.
Without using maxed Spotting I'm pretty sure I rode right past where the lair was hiding many times. Yours too may be in a strange spot (Mine was in a cluster of trees in the middle of the Tundra.) Hope this helps
Comb those bandit infested lands, Best of luck!
