Parts books
The best resources are the Buick Master Chassis Parts Book and the corresponding Body Parts book. Attached is a cover shot of a typical chassis book from '63 which has over 1200 pages. I used the '72 versions on your car. The '72s are available online at
www.wildaboutcarsonline.com. They are excellent at showing crossovers to earlier and later models. One drawback is that these have been digitized during scanning of paper originals. Some of the detail has been lost in scanning tiny print, fractions, and chart graphics etc.
The year-specific 1968 combined parts book is tremendous also. Cover shot of the 700 page book is attached. This one shows every part available on a '68 Buick at the time they were
built before any revisions or cancellations occurred. The ability to find year-to-year crossovers is limited.
Once the part numbers are in hand the next step is to Google "Buick xxxxxxx" using the part number. This will find parts on eBay and many vendor sites. Then I Google "GM xxxxxxx". This will find more items for sale and pull up crossovers to other GM brands. It also searches a bunch of GM parts books in the
www.gmpartswiki.com site Those volumes sometimes discover part number supercedures, prices, and discontinuation dates. It also searches through Chevy, Olds, and more recent Buick parts books. Each GM division apparently compiled their own data, so bits of information on a part show up in an Olds catalog that are not shown in Buick.
Secondary resources compiled from the original Buick data are useful and less expensive. It is easy to pick up MOTOR's and Chilton' Flate Rate manuals, A-C, DELCO, and other supplier catalogs.
There are mistakes in all of these resources (including me). The closer you can stay to the "original paper" source the better. New errors get created during recompiling and old errors frequently perpetuate into later secondary sources.
Buicks are are a little off the beaten path in the old car world. Production however was plentiful with Buick frequently coming in fifth, fourth, and even third in the yearly sales race. Chevy and Ford have long dominated the hobby to a degree even more pronounced than their share of production would indicate. Those who have been around a while remember Buicks carried a lot of prestige, being second only to Cadillac in the GM brand hierarchy.