come by

1.  Acquire, obtain, as in A good assistant is hard to come by. This usage, dating from about 1600, superseded the earlier sense of acquiring something with considerable effort. A variant is come by honestly, meaning "to obtain in some honorable or logical way." For example, I'm sure she didn't come by that large bonus honestly or He does have an unusual gait but he came by it honestly; his father's is the same.
2.  Stop in, visit, as in Please come by whenever you're in the neighborhood. [Late 1800s]

Definition: acquire
Antonyms: give, lose, miss

The verb has 2 meanings:

Meaning #1: visit informally and spontaneously
  Synonyms: drop by, drop in

Meaning #2: obtain, especially accidentally