One paper has them on KSD-AM St. Louis in 1926. The Buffalo express has them on WJAR-AM in Providence at 8:00 PM on Wednesday May 26th 1926. The Chatham Courier lists them on WSAI-AM, Cincinnati and WTAG-AM Worcester both at 8:00 PM on a Wednesday of 1926. Even a layperson would know that clearly their program was syndicated after finding these scant references.
"These concerts are presented by the Shinola Bixby Polish Co., with the Shinola Merry Makers. Mr. Green plays the Leedy xylophone, marimba, vibraphone, harpaphone, chimes and bells and the Leedy Mfg. Co. is featuring the Shinola concerts in its advertising."
That's what led me to a dissertation by one Ryan Lewis Green. It runs over 600 pages and is so detailed I dare not give it a fleeting quote. I just recommend you read it in it's entirely [link here] and I'll quote at legnth here the relevant passage:
"By 1926, Joe Green’s Marimba Band was already quite well-known “to the air folks” on the Eveready Battery Vaudeville Hour that broadcast weekly from 9:00-10:00 p.m.; however, it was the Shinola Merry-Makers radio show that truly marked the Green Brothers successful switch to radio. The Shinola Merry-Makers were the house orchestra for radio broadcasts sponsored by the Shinola Bixby Polish Corporation, a group that was essentially the Green Brothers Novelty Band. By the end of March 1926, “George Hamilton Green and his orchestra” could be heard every Wednesday evening from 8:00-8:30 p.m. on a long list of stations on the east coast and into the Midwest..."
Joe Green was born in Omaha, Nebraska in 1892. So he was 34 years old by the time the Shinola Merrymakers Joe played the xylophone, drums and timpani. Long before Shinola, he was playing Sousa on Victor Recordings. I own a few later diss recorded as Green Brothers Novelty Marimba with his brother George. More here.