You can get Natty's bz maps at bzscrap.com. CmptrWz posted a direct link below. Natty said there are a few maps that were designed for 2 teams. Those maps may need some tweaks if you plan on playing those maps with more teams than two and natty says you are welcome to make the tweaks. Natty says some of the maps use some tilesets he created and that you are free to use those aswell.
http://www.bzscrap.com/maps/Battlezone/nbClassicBZmaps.7z may be a better link now.
I'll delete the ftp link now that you have it on bzscrap.