I have seen a few references to this during some research, Particularly relating to American stockpiling of chemical weapons for a final 1919 push. I'm interested in learning more, but preliminary searching hasn't really borne any fruit. If any of you have any information or sources, I'd love to hear.
The United States did plan to make use of a new chemical agent, Lewisite, and this was being stockpiled shortly before the war ended. Considering the large scale use made of poison gas in 1918 by both sides, it is highly likely that gas would have been utilized to support Allied attacks in 1919.
Joel A. Vilensky has a book called Dew of Death: The Story of Lewisite, America's World War I Weapon of Mass Destruction; haven't read it myself and I don't know how I feel about the title, but if your looking for a source then there's one. Seeking Victory on the Western Front: The British Army and Chemical Warfare in World War I by Albert Palazzo is also a good source for Allied use of chemical weapons, in this case by the British.