There's an auction for a bronze/brass Galbraith Lyle-style cannon running on ebay.
I contacted John (cannonmn) to see if he might be interested in it, and also to ask if he thought it was a real one (maker's name on muzzle is stamped with an incorrect character). John indicated that he believes it's a repro, mainly because of the incorrect marking which would never happen on the real deal and the poor finish on the bore. He says that originals always have a nicely honed bore.
Anywhoo, I bid on it early when it was low, thinking it would at least make for a neat display after me and my good friend Brasso fixed it up. Now it's at $1200 with 20 bids and I imagine it will be higher when it closes.
Caveat emptor...