I had exactly the same problem on my campaign, unending peace. Couldn't find a lord to send me on a provocation quest.
Diplomacy mod allows you to try persuading your king to wage a war on a faction. you''ll need a good relation with him tough (20+, which I admit I was lazy and cheated to increase it). I managed to trigger a war for my benefit this way.
After the mod is installed just copy your game saves (usually in Documents\Mount & Blade Warband savegames\ Native) and paste it to the newly created diplomacy save folder ,just near Native.