I always check Ebay first. You never know what you'll find there. Great place to buy and sell items. If you really want something bad, make sure you bid the highest amount you are willing to pay for that item instead of just entering the next bid increment.
Try Amazon, Paracay, Sailnet, Landfall Navigation, West Marine, Defender. These are all catalog based merchants. I have bought books and guides from them all at one time or another. I hope these help.