I think finding someone who makes an affordable replacement is low for an older inexpensive rifle like this. A quick look on eBay shows that a variety of parts (including the stock) are available.
But my initial thought is that since the stock is fairly plain, I would not let a lack of woodworking skills dissuade me from getting out a saw, a plane & a rasp and making my own replacement. In my opinion, this is exactly the type of project to get a block of walnut & using the originals as a template, create a replacement. I think not only would it be a fun thing to do, but it would keep the family nostalgia part of the rifle going if a family member made the replacement parts.
