It seems like you did locate them, I can order them directly from that site, only bad part is the outrageous shipping charge. As for car-part.com, it won't let me search just for a Cadillac Fleetwood in my area, I need to use their dropbox to find what I'm looking for and it isn't specific enough. Unless I'm using that site incorrectly?

Select 1993 in the first box, then for the drop down look for Cadillac Fleetwood (1980 Up)

As for the part, you most likely won't find that part listed, but you should find the cars, so you know what salvage yards to check with, I am pretty sure most use that site, not all but most.

you should be able to fhttp://www.clipsandfasteners.com
just type GM in search box

a lot of guys use this one GM Garnish Moulding Fastener 1/2 Wdth 5/8 Height

Turns out going in to the GM dealer makes a huge difference, their response went from "The part is discontinued so we can't get the part number or the part" to "Let me print off the sheet. Ok it goes to these pieces? Ok here is the part number and a list of GM dealers near us that have it in stock"

I now have ten of them on the way to my house. Only $0.74 each and no shipping. Certainly beats the $50+ that GM website wanted haha. Oh and for the record it was number 56 and 42, he said they are the same. Thanks for all the help guys.