What you have placed in quotation marks is not from "The Lottery" itself. I am going to assume this is your writing prompt, a brief summary of what might be an external conflict, and I've revised it somewhat. Since any conflict that is not an internal conflict must be some sort of external conflict, I would have to say that there would be a conflict between Old Man Warner and the town if he were to be the one chosen to die, and there would be a conflict between him and tradition in that event, too.
The sole protesting voice is Tessie Hutchinson. She first protests when it is her family group chosen, then protests when her daughter is not considered part of the family group, thus increasing her own odds of being chosen, and then protests again when she is selected for stoning. It is fair to say that there is a conflict between her and the town at this point, and the same conflict would be between the person chosen and the town, no matter who is selected. If that were Old Man Warner, he would probably be complaining loudly. One might be able to lead a willing scapegoat out into the desert, but once one is sacrificing a human, a conflict between the sacrifice and those doing the sacrificing is going to be inevitable.
Another way to view this as an external conflict might be to view it as a conflict between the person chosen and tradition, with similar reasoning. Everyone, including Old Man Warner, is completely on board with this tradition of stoning someone to death once annually. But as we can see from Tessie Hutchinson, this respect can dissipate very quickly when the tradition is about to kill a person. Old Man Warner is fully in favor of this tradition because it has not cost him a thing. If he were the winner of the lottery, he would quite likely find himself in conflict with tradition.