I've come across it in the 15th episode of the 8th season the Walking Dead. Here is the context:
Eugene: If Negan needs bullets to end this war,
then, by ginger, he's gonna get 'em.
All of 'em.
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From an article I found online:
By George! By golly! By ginger! By gosh!: Basically a posh old version of OMG! The mild oath or exclamation dates from the early 1600s, when “George” and the other g-words were used as substitutes for God to avoid blasphemy.
So this is a way of saying, "If God wills it," without violating the commandment against "taking God's name in vain."
This phrase sounds distinctly old-fashioned, almost to an absurd degree, to modern ears.