I have seen replacement parts for that filter at Pet Warehouse's online store but i beleive most of the parts you are looking for will be available at your local hardware store. Home Depot has a great selection of plumbing parts.
I also have a Fluval 404 that i have been very happy with and the only part that comes to mind that you might need to special order is the impeller cover inside the canister itself. When you go to the hardware store you might be suprised to find that the employees know just what you need because there have been other "reefers" shopping there also =).