They probably don't make one for the oil pan because it's pert near impossible to keep that thing from leaking without a dab of RTV at each corner. Even then, it's iffy. My front corners on my 2012 are weeping a little bit and I was super careful when I put it all back together. Se la vie.
They don’t make one for the oil pan for our trucks because they don’t make oil pan gaskets period. Their tag line is “ The worlds best transmission and differential gasket” and that’s all they make unfortunately. The RTV is a design feature of GM because there’s a small gap at each of those corners where the front and rear covers mate to the block.