The International Brotherhood of Teamsters (IBT) archives in Washington D. C. includes records from dozens of teamsters locals, including four (4) digitized Belleville IBT Local 50 ledgers.
Publications, convention proceedings, documentary materials from the various IBT departments, trade divisions and area conferences, photographs, films, and video/audio tape reels and cassettes round out the collections housed at George Washington University in Washington D. C. (GWU). Its collections list may be found at https://library.gwu.edu/teamsters-archival-collections.
Resources
Belleville’s IBT Local 50
Search the Internet Archive (https://archive.org) for “IBT Local 50” which will bring up the four ledgers for the years 1898–1899, 1904–1905, 1910–1911 and 1913–1914.
An index in the front of each ledger may not be complete. The ledgers mostly outline the fees and initiation date for each member and sometimes a residence which may be helpful between census years.
The International Teamster, The Official Magazine of the International Brotherhood of Teamsters, 
Chauffeurs, Stablemen and Helpers of America, is digitized for 1912–2015. Copy/paste this title: The International Teamster, The Official Magazine of the International Brotherhood of Teamsters, for books at the Internet Archives, then click the Teamster 1912–2015 image for the available issues.
The 50th Anniversary of East St. Louis Local 729 was chronicled on 10 September 1959 in its trade newspaper. An index to that newspaper issue, “Business and Personal Names in the Southern Illinois Labor Tribune,” is found in the St. Clair County Genealogical Society Quarterly, Volume 35 Number 3, pages 117–132. Order this issue from SCCGS.
The 10 September 1959 newspaper issue may no longer be extant, however, some newspaper clippings in Box 2 for that year are available at the State Historical Society of Missouri Research Center-St. Louis. Here is a preliminary inventory of the 89 boxes in the ST. LOUIS / SOUTHERN ILLINOIS LABOR TRIBUNE RECORDS collection.
The Southern Illinois Labor Tribune (East St. Louis, Ill.; Saint Louis, Mo.) newspaper is on microfilm circa 1966–1970, available at the Abraham Lincoln Presidential Library, Springfield, Illinois, and the State Historical Society of Missouri, Columbia, Missouri.
Teamster Collection List at GWU Though the database at this link is sometimes “glitchy,” records for East St. Louis Local 729 and New Athens Local 576 apparently are at its archives. Contact the archivist for information if the database is unavailable.