Marshall and all,
I didn't spend 40 + years in the parts business to not learn something. What you are looking for is offered by AUVECO which stands for Auto Vehicle Company. I've carried their products for years. Here is their description and part # (2610) in the catalog: "MONOGRAM LETTER PANEL SPEED NUT". Application is: BUICK ALSO GENERAL PURPOSE.
The way these work is you insert them into the opening on the hood and press until seated via the flange and then push the letter into the clip. They come in a box of 100 but if you can find a source local to you I'm guessing you can buy what you need. For my money buy the box and keep them and maybe down the road you can help someone out.
Hope this will be of some assistance,
John Lazenby