Jonnson might be available in the USA. They ship to the UK, but you have to email your order and it takes several months. My wife loves them, they are the only shirt she has found that fits her well. Azulwear have a great selection of bush shirts and will ship out of South Africa. I have a friend who spends a lot of time in Kenya, obviously not hunting. He swears by Teesav shirts and wears them at home. He has one that has been worn a couple of times a week on his farm and is 40 years old. I ordered a couple, but they never arrived. My friend gets someone in South Africa to post them to him.@Dewald - Both great shirts with a caveat. The Jonsson shirts are not available in the US and the Stevenson Hamilton ripstop has been discontinued.
All it really means is that we need to leave some space in our luggage and hit the store when we arrive in town for safari.
I really like the Ruggedwear Shirts, they are really tough and surprisingly cool, given the weight, but the heavyweight ones are only available in light colours, so you have to dye them. I am not keen on the epaulettes either, I can't see the point of them.
This is my favourite though: