FWIW & IMHO:
If you are looking for used ones, they occasionally pop up on this forum section from time to time, and on E-bay parts occasionally. If you are looking for new ones, they are available from the dealers under GM PN 25518704. I believe that dealer list is about $ 85.00 or so, pretty pricey. GM Parts Direct has them under the same part no for about $ 50.00 + $ 10.00 S & H. I purchased a brand new set for about $ 265, shipped to my door, from Michael mcCoy, (G Body Parts). I believe that he is a supporting vendor on this site. HTH