IC:D&D 3.5 Dragon Hunters
Make it a dedicated mercenary company that specializes in dragon-hunting. They send newer recruits (read: low-level) out to chase down hatchlings that have been spotted on the loose. It would keep the draconic population from taking root in an otherwise clear region, give newcomers field experience, and weed out those who don't make the cut.
(In other words, have a pool of low-level characters ready to step in for the inevitable PC death.)
As they gain experience, the hunters would start going after more mature dragons who would be in the middle of staking out a territory claim. That may entail taking out several dragons who are fighting over a stretch of land. Not necessarily fighting multiple at once (though that can happen), but each time they take one out it would effectively make the others stronger. The last one would fight hardest of all, because beating these humanoids would guarantee its claim.
At higher levels, they might even have to defend the mercenary company's headquarters against dedicated dragon attacks, as the older ones decide the company's a real threat.
The company could have the cooperation of some good-aligned dragons, who help fight the evil types in exchange for a share of the resultant treasure. Or they might decide that all dragons are a threat, good or bad, and therefore hunt down anything draconic.
Depending on the company's attitude about it, they may even go so far as to oppose anything with draconic ties -- including most sorcerers, and anything with visible draconic ancestry.