I do my own usually, but since it seems you want a keg full, it is probably better to buy. I just keep a shit ton of spices in my house so I can mix up whatever I feel like at the moment.
some sort of mexican beer, S&P, cumin, cilantro, garlic, lime, chili powder. I am sure im forgetting a couple things but it's damn good.
I don't mind A1's seasoning as a base, then add a couple things to spice it up a bit. I got my gf's dad a rub kit, has rubs for pork, chicken, beef, seafood. I will get the name & give it to ya.
Or Weber's coffee rub isn't a bad way to start.