The meaning of the verb "to come by"

[Pivosz]

English Language Tests, Intermediate level

ESL/EFL Test #139 "Idioms with the phrasal verb come", question 2

I just can't seem to be able to find a good personal assistant as they are so hard to ..........

(a) come by
(b) come back
(c) come out
(d) come across

English Language Tests, Intermediate level

ESL/EFL Test #139 "Idioms with the phrasal verb come", answer 2

I just can't seem to be able to find a good personal assistant as they are so hard to come by.

Correct answer: (a) come by

Your answer was: incorrect
I just can't seem to be able to find a good personal assistant as they are so hard to come across.
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Hi,
What's the meaning of the verb "to come by" in this sentence?
Thanx in advance.

[Mister Micawber]

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to come by = to acquire, to find.
.
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Native English teacher at Mister Micawber's