One option is to get some perlon (non-woven) or other cheap fabric and make your own pattern. A pattern is nothing but a model. The idea is first to make a full scale model of the inside shell. Modify it until it fits right, making allowance for the thickness of the insulation. Then make a model of the outside shell, again making some allowance for the insulation making the outside shell larger than the inside shell. Stitch is with a basting zig-zag by loosening the tension of the top thread enough that it still stitches properly without tangling. You can use cheap Walmart continuous-filament batting to test. Then make a model of the collar. This is a two-hour job- a lot quicker than waiting for a pattern to arrive. has a vest pattern,
Or Google on insulated vest patterns: for example