The "Four Yorkshiremen" was never shown as part of the TV series, as far as I remember. I believe it was performed on stage at Drury Lane Theatre, and was recorded as part of the LP "Monty Python live at Drury Lane".

Likewise, the "Last Supper" sketch was banned by the BBC on religious grounds and never shown. It was performed as part of the Amnesty International benefit show, "Pleasure at Her Majesty's", and featured Jonathon Lynn as Michaelangelo and John Cleese as the Pope.

The Pythons did indeed show some brilliant individual sketches, but in both the TV series and their films ("Monty Python and the Holy Grail", and "Life of Brian"), what made them immortally funny was the insane but coherent continuity between the sketches. ("Meaning of Life" perhaps pushed things artificially a little too far but the musical sketch "Every sperm is sacred" deserves a medal on its own.)