Back in 2002 I created a little website to host some maps I made. Well, it's still there if you are looking for some custom maps.

http://the-maproom.com The Maproom.

Mostly just MP maps, but the map Big Islands has a singleplayer mission packaged along with it titled, "Wolfshead Narrows". Comes with some mission tactical info and is a challenging mission. If you have more than 12 (?) custom SP missions, 'Wolfhead Narrows' likely will not show up since the title begins with a 'W' and the maps are listed alphabetically. The total number of SP missions in the instant action menu is hard-capped is the reason for this.

Good Luck.

-Lightfoot