Hello, where can I buy a cheap OEM Acura TSX water pump?

Your best bet would be to just go to your local O'reilley's auto parts store. You could also trya href="http://www.rockauto.com" rel="nofollow"http://www.rockauto.com/a If you don't mind waiting for shipping. However in my personal experience when dealing with Acuras, it's much better to go with Parts from the manufacturer. When I did my water pump from a parts store, the bolt holes didn't line up properly, and I ended up having to go to the dealer for the part anyway.