I recommend avoiding turtlesale.com and turtleshack.com. Same company, different name. They have pretty poor husbandry practices, and often send turtles missing toes or tails, or with shell rot, fungus, RI, or other medical problems. They have an almost universally bad reputation.
Turtlesource.com has very good quality animals, but you're paying a premium price for them.
Kingsnake is hit and miss, because essentially anyone can post there. The previous link is to Paul V's listing for musks, and I can vouch for him, he's among the best of the best.
Josh H