I would love to be able to get ahold of that keg of beer prop from the movie or the hat or suit that Cagney wears in the end before he goes after Schemer Burns.
Do you think they are still around collecting dust in some prop warehouse?
There are sites online that sell movie props/costumes. But 1931 era may be hard to find as they probably didn't think of selling the costumes, etc. or if they're around, they're porbably in a film museum. It would be cool to have something from an old Cagney film, I agree.
There was recently a TCM/Bonhams auction of props and clothes. They auctioned a James Cagney overcoat from "Hello Frisco" 1935. Since I'm about Cagney's size, I would have liked to bid on it. But alas $3500 was a little too pricey for me.
The best places to look for film props/costumes from the 30s and 40s would probably be with the grandkids and great-grandkids of studio employees. May I bone your kipper, Mademoiselle?