I'm pretty sure the gas station at the fish creek exit sells bundles. Just get a saw and cut some down timber- you don't need a permit for that. Or just walk around and collect it- its free, will get your blood flowing, and never ending.
I think that you should also be able to find some athe grocery store in Superior (just north of I-90). Wiht all the campfire restrictions this year they probably didn't sell out. I would also look for some slash piles. usualyya grat place for fire wood.
I've been to Kelly Creek CG at both the end of September and first weekend in October. At best, deadfall firewood has long before been picked up by previous campers. At worst, the few sticks you are lucky enough to find may be soaked if it's rained before you arrive.
Not sure about you, but I didn't drive that far to waste valuable fishing time cutting and splitting firewood.
Last time, I went with two other guys in a big Chevy Silverado crew cab with a shell that was half full of dry, split wood we hauled over. We burned every stick of if over the course of four days and three nights. It rained hard the whole second day and froze the next two nights.