Corid (amprolium) is a good treatment for it, and there is no withdrawal time listed for it in the literature for slaughtering. Even if there was it's usually 2 weeks so if you treat this week you would be OK by the end of November, anyway.
If you can't find Corid, you can use Sulmet. Sulmet DOES have a withdrawal time for slaughter, which I THINK is 14 days, but don't take my word on that, check the bottle.
If one bird has it, the rest might have it, too - you should treat your entire flock. Corid is "safer" if you have egg-laying going on, as you should still be able to eat the eggs. If you are just raising meat birds and want to slaughter at the end of November, then either Corid or Sulmet should work. Hope that makes sense. Good luck!