http://www.harriets.com/wwiipatterns.htm

Though this one is for "German" enactors, the pattern does go up to size US44. It's an expert, tailoring type pattern though. (and unlike Smoke and Fire, I've never ordered from these people, so can't say anything re their customer service).

Also, I thought I remembered an Ike jacket in the Folkwear line - but it was a 'bush' jacket from Austrialia, and is far too long for what you want. (I'm SO going to make a Drover's Coat, though!)