It wouldn't be difficult to find them at all. In most cities, the illegal immigrants live in certain neighborhoods, hang out on certain street corners or Home Depot lots looking for work, etc. Believe me, local law enforcement *knows* where the illegals are. They do nothing about it because it's a *federal* responsibility.
The laws need to be changed so that local law enforcement can pick up illegals & take them to federal offices, drop them off, and let the feds do the deportation. If Mexico doesn't like it, tough.
Even if the law changes, law enforcement will not do it, because they say it destroys their channels of communication with immigrant communities. That's why it is laughable that the INS wants to create a database of illegals with deportation orders in the hopes that local LEAs will help round them up and report them.