K&N is one of the oldest Yamaha dealers in the US. They even had a 1971 Yamaha XS650 headlight in stock for my friends restoration. You should have seen the box it was in. Easy to tell it had been on a shelf since 1971. All the cosmoline had dried to a solid mess. Had to clean up. :biglaugh:
They have had a lot of parts that show up on parts lists as no longer available including OEM carb parts for a 1981 650 Maxim. If you can't find an OEM Yamaha part, give them a try. They may have it somewhere in their warehouse.