flowerbug
Garden Master
Not surprised you haven't found it. As I said, it is a VERY old joke, as in it dates from the 1800's (or maybe earlier). I only know it because Dover Books publishes (or did publish) a re-print of a 19th century joke and riddle book. (I think it was called 1000 Riddles, Enigmas and Conundrums).
Anyhow, the answer to "Why is a chicken pot pie like a gunsmith's shop?" is "Because they both have fowl-in-pieces." (fowling pieces are a kind of small gun used for bird hunting back then.)
Another one (the only other one I remember that wasn't a rebus, and hence unshowable here [since I can't draw])
was
"Why will a one winged chicken always fight with a two winged chicken?"
"Because there is a difference of a pinion between them."
haha!