I think you'll struggle to find any that are 100% cotton I'm afraid. I find the Van Heusen 'Aviator' shirts very good and far better quality than anything else on the market.
I bought most of mine in the USA when I was there and struggled to find anyone selling them in the UK, so when I needed more I mail ordered them from the US. They are a thicker material and far longer lasting than anything else I've seen.
Good luck!