Luthiers Mercantile International, Inc. - an online guitar maker’s supply. They have a large variety of tonewoods and hardwoods, and just about anything else you could possibly need to customize your guitar.
Eisenbrand Exotic Hardwoods - another good hardwood supply, with good quality exotics, though they don’t cater specifically to instrument-making.
Stewart-MacDonald - guitar shop supply with a good selection of woods. They also have a lot of materials for electric guitars, violins, and other stringed instruments, and several building kits with some of the harder steps already done for you.
