2008 STS Oil pan cover - missing nuts UPDATED
 

HI, I am a new member. I just bought a 2008 STS w/3.6L. Nice car so far. But I went to change the oil yesterday and found that the cover under the oil pan was onlly being held on by two bolts and a zip tie! It looks like the nuts for this cover clip into openings in the frame rail and all but two nuts are missing. Where can I find replacements? The nearest Cadillac dealership is ~30 miles away. Can they be ordered online? From another GM dealership? I have searched online but since I don't know what this type of nut is called I have had no luck. Thanks for any help.
UPDATE: I found what I needed at https://www.gmpartsgiant.com/ . They seem to have the model specific parts that otherwise a dealership would have to order. I hope that helps someone.