People seem to use Chris Peers' Contemptible Little Armies a lot.

There is a free set of company level rules on the free wargames rules web site.

Don Featherstone did a set for German SW Africa as part of his Wargamer's Newsletter rules collection - Athena published the collection and you may be able to track it down.

Hope one of these would work for you.

I've tried to post this with links four times but the forum keeps saying spam has been detected. Google will be your friend to find them.