What is "to hearken out"

Hearken \Heark"en\, v. t.

1. To hear by listening. [Archaic]

   [She] hearkened now and then Some little whispering and soft groaning sound.
   --Spenser.

2. To give heed to; to hear attentively. [Archaic]

   The King of Naples . . . hearkens my brother's suit.
   --Shak.

   To hearken out, to search out. [Obs.]

   If you find none, you must hearken out a vein and buy.
   --B. Johnson.