If you're an e-bayer, try doing a search for "Willis & Geiger".

They're an old safari outfitting company that was started by some friends of Teddy Roosevelt; they made a lot of items for his African trips.

Anyway, they had some great light-weight safari-type shirts, and you can sometimes find them on e-bay. I've sold a few of my W&G items on e-bay (for top profits, too) but I'll never part with my safari shirt as it looks great with the kilt.