There's a guy in a neighboring town advertizing a B body rear end from I believe a 1973 Pontiac wagon, I don't know if this is the same unit as used in the Buick. He did say it was the 9 3/8 ring gear. He was asking $175 for the complete rear end. I don't know if he'd be willing to pull the carrier out and ship it to you, but here's his web site if you want to check it out. http://jjsmusclecars.com/parts.htm He advertized this in Medford Oregon Craigslist on December 28 John
Saw one last summer in Cleveland area. Don't think he'll seperate it. If you want more info, PM me and I'll fill you in. I know it's out of a Riv GS.
Careful on that Pontiac rear, I got one shipped to me and it wasn't the same. It came out of a 73 Catalina with a 455, and it was smaller than the Buick's 9 3/8, just double check if you're getting it.