I hate to see a good complete car that is rust free get parted out. There are still TONS of old cars in junkyards on the west coast. It just takes some phone calls to the venders who advertise in Hemmings Motor News to find what you are looking for.
For used parts on my 1960 & 70s Buicks and Oldsmobiles, I've had good luck with Pacific West Auto (818-897-4141) and All American Classics (
http://www.allamericanclassics.com/). I've bought bumpers, trim, etc from both and been very pleased.
For convertible top parts, check with Hydro-E-Lectric (
http://www.hydroe.com/). They should have everything you need.
As far as disc brakes go, check with Disc Brake Mike, he sells a conversion for your car:
http://www.discbrakemike.com/
On the rear bumper, it is AMAZING the repairs that modern bumper replaters can do. They will patch in new steel, metalfinish it smooth and chrome it like it was never damaged.
For a lot of the soft goods (window felts, weatherstripping, carpet, etc), Chevrolet Impala parts are an exact substitute. I replaced the weatherstripping and rear package tray on my '66 Buick LeSabre with '66 Chevrolet Impala components and all were an exact fit! I like C.A.R.S. (
http://www.carsinc.com/), as they sell quality components and are in my neighborhood!
Enjoy your classic Oldsmobile!