Yamaha Marine parts locator:

http://www.yamaha-motor.com/outboard/parts/home.aspx

Manufacture date 01/01

Model Number F50TLRZ

Prop Pitch 11 3/8 X 12    Propeller info               http://www.boatfix.com/how/props.html

An Honest Parts Guy:

A good after market parts guy, Master Tech :  http://www.maxrules.com/fixyamahaindex.html

And a good Yamaha Parts Guy in Florida : http://www.yamahaoutboardmotorpart.com/pages/parts/viewbybrand/default.aspx

Tech tips I have found useful :

Changing the impeller :    http://www.thehulltruth.com/shipyard-isl-marine-engine-parts/64864-pics-yamaha-water-pump-replacement-f115.html