I do know that the much better construction is "he wished he had met her a year before", but is the construction "he wished he would have met her a year before" acceptable?
Would have instead of had in a unreal conditional/subjunctive is found in informal spoken American English and in printed or digital sources close to it.
Did Albert Einstein really say he wished he would have “studied the Talmud?” — Quora question.
In numerous talks with his wife, the subject of school kept coming up, and many times he found himself mentioning that he wished he would have gone into medicine. — Beacon Health System (IN).
Jack listened to the message, only to find it was his credit card company letting him know of suspicious charges. He wished he would have answered. But how was he supposed to know that was a call he should have answered? — A Better Credit Fraud Alert Experience, Neuster.com
While one grammar source condemns this periphrastic usage as a error, I think it’s more a question of register: acceptable in most informal speech and writing, but not in more formal registers. I suspect the usage arose in analogy to should have, as in this example, and could have.
In British English this is not acceptable in any register although the meaning is clear.
It has specific overtones, namely it suggests the speaker is a native speaker of a language where this use of the conditional in the dependent clause is normal.
Although not true British English, there is a caveat: certain minorities may be comfortable using the conditional like this, and in particular Jewish communities, where some grammatical patterns seem to be influenced by German/Yiddish.