I have seen a number of posts here and on other forums asking for information on WW2 RAF officer's shirts and where a passable modern equivalent can be obtained from. In the past TM Lewin has been suggested and I have found that they do in fact make a shirt of very similar material but unfortunatelly the collar is of the modern semi cut away type. I have found a shirt on the link below (currently on offer for £34) that seems to be passable in terms of material and it is available in single or double cuffs. It does not have a detachable collar and it buttons all the way down, but is the best I have found so far.
I hope this helps.