Ibex is one, I have three of their jerseys and like them fine, Wabi Woolens is another, and is reported to be of very high quality, Joneswear is another, but is short on stock, and Smartwool has one now, but its a blend.

None of these are going to be cheap. I tend to recommend Ibex because I've been very happy with the jerseys that I have purchased from them.