You mean the electric fuel pump ? You could also try 1969 Rivieras at the scrap yard, they used the same electric fuel pump inside the tank. Access is through a little door in the floor of the boot. Or use a mechanical fuel pump instead, but you also have to change something in the electrical department if you do this. Has to do with ignition cut-off if the fuel pump isn't running, if I remember well ? Use the board's search function to find out more :TU:
Here is the source for a rebuild or a trade on a refurbished unit. $ 190 will get you one. http://www.v8buick.com/showthread.php?t=91071&highlight=riviera+sending+unit