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It is hard to look for they domains because so many people already are. Some people registered thousands of domains and listen for traffic on them for a few days. If the traffic is good they keep them. The rest they throw back. ICANN gets really anger when they see this. So Registrars will not like you either. In general there is no automated way to do this with out getting in trouble.
There are a few companies in this world that specialize in buying old domains and using the link traffic.
Adult sites are getting extremely good at this. Recently, after Canada3000 (a no frills airline) went under, an Adult content site picked up the domain.
Every official government tourism site in Canada incidentally linked to Canada3000. Not somethinng you really want potential tourists to find associated with you.
This is becoming a big problem and it pays to monitor and groom your links regularly.