This was often the bane of my existence in retail book life, especially after I started library school. The key here is entry points. You need a catalog with subject headings. That's where you really find out what's what and what else is out there. Does your public library have access to the WorldCat database? As the name implies, it's a huge international shared catalog. But barring that, what I came up with is looking for Louisiana in WWII and Earl Long, Huey's brother who carried on the family name in state politics. The short answer to your question would seem to be that Earl Long is what happened in Louisiana after Huey's death. It's said that the Long machine was still resonating until Earl's death in 1960 right after being elected to the Senate. So this book may give you a good grounding:
Earl K. Long: The Saga of Uncle Earl and Louisiana Politics
Hope that helps!