Here's two of my go to sites:
http://www.hodgesmarine.com/
http://thmarine.com
You can buy direct from Hodges Marine and I've seen them beat most prices on many occasions.
You can't buy direct from TH Marine but their stuff is good and they have a huge variety. Find what you want and then click on "BUY ME" and it will give you a list of distributors. But the best way to get the best price is to find what you want and then paste the Manuf. Part # into a search engine and look for the lowest price.