ToadMarineSupply.com sells Yanmar parts to the east coast
. I believe they are an authorized dealer. Their prices are about what you'd pay at a local dealer, but the convenience may be worth it to you.
I've found the Yanmar dealer network on the west coast
to be very frustating. Not only is the nearest dealer 25 miles from my home, they are often out of stock, requiring several weeks delay and a ridiculous shipping charge. Yanmar parts distribution needs to join the 21st century.