Fashion Sewing Supply.
Well, I knew I was ordering the hair canvas, but the fusible part turned out to be the surprise part.
Never mind though, instructions came with the fusible hair canvas, and I just went with it. As you can see, the lower sleeve part has yet another interfacing, and this one is Pellon 860F Ultra-weft. Also fusible. Seems pretty good, and is loosely woven.
And I used a sleeve head to support the sleeve cap and to help with the easing. The sleeves went in pretty easily with only one pucker that I had to fix.
And then on to the pad stitching for the collar. I had enough regular hair canvas, so used that. One of the problems I had with the collar was that as you stitch, the canvas can get pulled and bunched, and then doesn't go to the edges like it should. If you hold it with pins (which I did) you get repeatedly stuck. Ouch! My solution: