I'm not sure about what's available today, but back in the day I knew of 6 styles available for full size GM cars, not counting Cadillac which had their own specific ones. They were all the same basic size but had slight variations in each design. Some had logo's on the bottoms, while others were blank. Some had "chrome" upper portions with black bottoms while the others were all black.
I saw a NOS set of 4 solid black ones on ebay a couple months ago. TBH, ebay is probably the best place to watch for them.
How cool are the workers at your local auto parts store? Will they let you take several sets of guards out to the parking lot to match up the correct size to your car? Chances are good that you'll find an aftermarket set that will fit perfectly.