I know this is a long shot, but I am looking for some parts for my 58 Special. rear bumper gas door rear bumper ends (Special or Century only) back up lenses (mine are cracked) Fender ornament V with the spear bases hood center trim rear view mirrors rear window trim (Special or Century sedan only. The large rear window trim for 2 tone paint jobs) B pillar trim for a sedan day/night rearview mirror hood whiskers
I saw at least 2 '58's at Hidden Valley Auto Parts in Maricopa, AZ a few moths ago. Not sure if they have the parts you are looking for, but may be worth a phone call.
Know of a horde/stash locally. Have posted more details in the "cars and parts lead" section. southern new mexico
CARS LLC reproduces a lot of what you asked for. Here's a link to their catalog - 360COVER.QXD (oldbuickparts.com) CARS LLC - 908-369-3666
Hidden Valley was purchased by DVAP, to the best of my knowledge. DVAP has, or had, a Casa Grande yard, as well.