One thing Craig's list is good for is selling inexpensive detectors, say up to $150. Many potential buyers are people who've thought about detecting for years. One might team up with this person, offer assistance learning the detector if wanted.
Or just suggest going out detecting together. They & the people they know could possibly know of a not well known potential hotspot, or may have an in with a person who supervises places that are normally off limits.
Or if you want permission to detect peoples yards, you might have to offer them half the finds. If they don't amount to much they'll probably say keep them. You can offer to remove litter, return any personal possessions, etc.
Perhaps best could be offering to locate personal metal items with monetary or sentimental value, for small fee or coins found. Best wishes, George (MN)