Craftsman 580.750401 pressure washer replacement unloader valve and plug.

I recently got a craftsman pressure washer and I am in the process of fixing it.  It has a Briggs and Stratton Power Products 705274 Pump.  Upon inspection there is a nylon washer on the unloader valve that is cracked and the white plastic plug that covers the unloader valve is broke.  I am trying to find these parts to replace of find a suitable substitution.  Any information on this issue would be greatly appreciated. 
Thank you 
 Justin