From the look of the buttonholes it seems to be a standard Army jerkin with a shearling lining and a collar. He might well have got it modified himself somewhere.
Most of the WW2 ones on sale are a bit sad now but you can still buy very good Belgian army versions in unissued condition. They have brass buttons but they can be changed and are otherwise pretty identical.
No he would have had it done himself for sure. You could have yours shearing lined too of it's big enough.