These people can often recall unusual finds. Well worth trying. Owners and curators of old houses. Try asking people who live in, or care for old houses. A large number of finds from this source have already been recorded.
Builders are really the best people to ask.
Over half the builders spoken to so far for this survey have been able to report a find. Only a very small proportion of finds ever get recorded in a museum or archaeological unit. By asking as many builders as possible, a more accurate picture of the distribution and extent of these finds may be gained. Local libraries and record offices. Books on folklore in your area might contain the odd reference or two to folk magic finds.