I came across your and Mr X's publication
or
I came across you and Mr X's publication
I came across your and Mr X's publication
or
I came across you and Mr X's publication
CMOS 16th edition says in 7.22 that it depends on whether you mean the nouns as a single unit or as discrete units; that is, whether the object possessed is the same or different for those two nouns. Since you're talking about two authors responsible for a single publication, not two authors of multiple publications, the nouns are a single unit. "I came across you and Mr. X's publication" is correct.
But there's no question that it is awkward because it's in the second person. (Compare to this third-person sentence: "I came across Dan and Steve's publication.") Reworking the sentence is definitely the way to go.
"You" sounds wrong and "your" awkward. Turn it around: I came across "Charlie Manson reconsidered" by you and Mr. X.
According to Garner's Modern American Usage by Bryan A. Garner, correct usage would be, "'Thanks, Dad....It was through your's [read your] and Mom's hard work and guidance that I have come this far.' Ginny Rudy, "Traveling in Memory of Dad," Pitt. Post-Gaz., 26 Dec. 2000, at E3." (Here, the read version, which is your, is correct).
Singular unit when both parties are part of a single topic, transaction, etc.
example: 'You and your brothers'
You wouldn't say 'Yours and your brothers' Two many pocessions-there are not multiples of 'You'. Brothers is showing ownership of the 'subject'. You can't both have plural ownerships hence the word 'and'