Actually, he never gave up.
The week before he was assassinated included an interview with Gen. Dan Sickles (of the Wheatfield at Gettysburg), who had been down in Panama on an extended, confidential special embassy and had come back to report to Lincoln on what he had found. He was scoping out Panama for a canal. The concept was to send perhaps 2,000,000 emancipated blacks down to Panama to dig the Canal (this was pre-Walter Reed, so you can imagine what the casualties would have been), and then stay in the area -- the survivors, anyway -- and become the new residents of that country, a new Liberia in effect.
Sickles was talking to Panamanian locals and to the government of New Granada in Bogota. The U.S. State Department files that should contain Sickles's journals and daybooks have been gone through and filletted, according to FReeper GOPcapitalist, who did a search about eight years ago.
Lincoln's interest in colonization was very much alive and well on the day he died. There are no notes of his interview with Sickles, which took place about the 10th or the 11th, when of course the air was full of the good news from Appomattox.
I doubt that the plan was to send the Blacks to Panama against their will or as slaves.
One of my ancestors was among the founders of the anti-slavery Republican party in the state of NY and had no such plans for “negroes”. Instead, he hired two to work on his property in NY, as free men.
I had another ancestor who actually did work on the Panama canal as a train engineer. He loved it.
There is, of course, Benjamin Butler's conversation with Lincoln about colonization a few days before the assassination. Evidence has been found that Butler did meet with Lincoln during that period. See White House scheduling pass for April 11, 1865, found in Butler's papers.
According to Butler, Lincoln was worried about what to do with black soldiers after the war. Butler proposed to send 150,000 of them to Panama to dig the canal. Since they were still soldiers, they could be ordered to serve there. Butler said that Lincoln thought the idea had some "meat" in it and that he would discuss the matter with Grant.