Bodies (planets) with volcanism make it far easier to find these materials so when you search (on EDDB, for example), include that in the search parameters. Then scan them as you approach and land at the geological sites that your DSS will find. Try to land at a site that's lit by the star for the best experience compared to night vision green. It's fun to see some of the really cool planetary surfaces and features, even launching your SRV off the surface once in a while by driving over an ice geyser!