get a line on
Also, have a line on. Acquire information about something or someone, come to know. For example, Sue got a line on some possible tennis partners, or The realtor has a line on a number of vacant apartments. Similarly, means "provide information about," as in The librarian gave me a line on the books I would need. This idiom uses line in the sense of "a direct course." [c. 1900] Also see get a fix on.