One thing that some recruiters do is to ask “if you know somebody who may be a good fit” when in reality, they are asking you of you could be interested.

I typically do not bother to respond to blind solicitations from people asking me to fill out another profile. If they looking to fill a position, I’ll talk to them. If they are looking to fill their rolodex, I’ll pass.

Can you offer some suggestions as to how a “good recruiter” can come up with passive, qualified candidates for specific positions by a means other than referrals?
Fact is, a “good recruiter” works 90% (or more) referrals. “Good recruiters” don’t look at job boards like Monster, careerbuilder, etc. They are talking with people, establishing relationships, gathering referrals, etc..
I take offense to your statement about spending time “milking potential candidates for referrals.” If you are a “potential” candidate, that means I am not actively presenting your background to prospective companies. Why should I not ask you if there is anyone you know who may be interested in the position I am currently recruiting for?? Surely if you’ve been in the industry for any amount of time, you either know someone that is looking, or you know someone who knows people that are looking.
See, the relationship with a “good recruiter” goes both ways. I have many candidates that I have placed (some multiple times) that call me at least once a month just to see who’s doing what, where and why. They understand the “you scratch my back, I scratch yours” mentality and this makes it a mutually beneficial relationship.