Great American Gunstocks Can cut you a dropbox pattern. They charge an extra $50 for that. Here's one I had done a few years ago.
One thing though with this company, you need to inspect the blank when you receive it and if you don't like anything about it. RETURN IT. I used this company 4 times and 3 of the stocks were perfect. This one wasn't and I tried to fix it. Looking back, it should have been sent back and had it replaced.
Another option is what Z1R suggested. Add the drop to a pattern and have it re-duplicated. I'm redoing this rifle and this is the route I'm taking this time. You can personalize the pattern anyway you want. it's a lot harder, but more rewarding
Terry