Welcome to the Team!
The B-bodies are not as popular with collectors as where the smaller sportier Camaros and Novas were as such there is less demand for parts for these cars. GM as corporate policy used the same parts over and over again to build their cars so a part off another model or marquee made for several years before or after your car will also fit your car. Chevrolet was odd man out in terms of transmissions as Chevy had their own unique bell housing pattern not shared with the rest of the GM fleet. The good news was that Chevrolet made trucks which is a good source for heavy duty suspension parts such as brakes. The Corvette and the Impala all share a lot of parts in common up until 1996 when they broke away from sharing common parts and went after the super car market. The Corvette was a rebodied full size car originally and any go fast power train and suspension goodies were often retrofitted on the bigger car due to it's increased weight as it became more luxurious over the years. Both cars stole parts out of the truck parts bins to use bigger brakes and stronger suspension parts.
But that won't help you find sheet metal or interior parts specific to the full size cars as you are dependent upon the aftermarket for those parts to be remade. Good news here is you own the second most popular car year made after the 1964 model year (excluding the tri fives which are fully reproduced).