Outboard parts in Baton Rouge Area

Where do you buy parts for an outboard motor in the Baton Rouge area? I have a 2004 Mercury 200 EFI 3.0l and need to replace the poppet valve and impeller. For some reason the poppet valve for this motor does not come as a full assembly like most. I have to assemble the various parts but am having difficulty with determining the exact part numbers as it seems Mercury likes to update them on a random basis. Any recommendations or advice is appreciated.