Stewart-MacDonald everything for building and repairing guitars.
Stewart-MacDonald’s site is very complete, and has a lot of guitar pieces, like nuts, saddles, bridges, truss rods, finishing supplies, even body, necks and wood to build your own guitar!
Also, has a newsletter, called by him “Trade Secrets”, that give you tips to repair some things about your guitar. You can suscribe to the newsletter here.
If you want to see a real example click here.