When Grant and Lee sat down, what did they contractually agree to?
MacArthur vs. that poor guy that got kicked to the curb with the top hat.
www.ourdocuments.gov/doc.php?flash=false&doc=39
But that wasn’t a treaty – just a military surrender document for Lee’s army.
The surrender of Japan to the United Nations is also at that site – document 80.
As t-bonham says, neither of those documents are treaties. They are just surrender terms.
There was never a treaty to end the US Civil War. As far as the Union was concerned, they simply supressed an insurrection. They never recognised the Confederacy as a sovereign entity, so who was there to conclude a treaty with?
In 1945, the bloke in the top hat and the guy in the implausibly large peaked cap signed surrender terms. The Peace Treaty didn’t come along until 1951, and neither Top Hat nor Peaked Cap was present on that occasion.
Your main question seems to have been answered.
An excellent place to find legal and diplomatic documents like treaties, especially (but by no means only) those relevant to American history, is the Avalon Project at Yale Law School. I often make use of documents from this site in teaching university history classes.
I imagine the National Archives would be a good source as well.
Slightly off-topic, when I visited the National Archives I was delighted to see the actual Webster-Ashburton Treaty on display in the exhibition area. I wrote a term paper about this treaty in high school.