coho911 off of outdoorsmenforum does a bunch of this. If you wanted to give us an idea of what corner of the country your located we could probably point you to someone more local though.
I did have someone in Calgary make some stuff for me, I really liked the butt stock with bullet loops, but the sling, although cool and different, didn't really get built with contours ideal for a sling, the fella doesn't have experience hunting and didnt really understand a couple things, but it works.
If you do get some stuff built, I would get heavy full grain leather for the sling with maybe a thumb loop, and get a buckle or loop on the butt stock cover for sling attachment.