Has there ever been a just man?

Yes

Nephi, Jacob, and Joseph, Sam, and Shiblon were just and holy men.

Nephi, Jacob, and Joseph, and Sam ... were just and holy men. Alma 3:6

Shiblon ... was a just man, and he did ... keep the commandments. Alma 63:1-2

And so was the other Nephi (the son of Helaman Jr.)

We know our record to be true, for behold, it was a just man who did keep the record. 3 Nephi 8:1

There has never been a just man.

For there is not a just man upon earth, that doeth good, and sinneth not. Ecclesiastes 7:20